Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $235.70   13.114%   $266.6097   $266.61   $266.60   $266.60  
  Purchase #2 $116.75   11.668%   $130.3724   $130.37   $130.35   $130.40  
  Purchase #3 $238.84   12.293%   $268.2006   $268.20   $268.20   $268.20  
  Purchase #4 $229.98   8.552%   $249.6479   $249.65   $249.65   $249.60  
  Purchase #5 $197.34   10.547%   $218.1534   $218.15   $218.15   $218.20  
  Purchase #6 $117.34   3.546%   $121.5009   $121.50   $121.50   $121.50  
  Purchase #7 $227.85   13.871%   $259.4551   $259.46   $259.45   $259.50  
  7 purchase totals = $1,363.80       $1,513.9400   $1,513.94   $1,513.90   $1,514.00