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 $134.33   12.604%   $151.261   $151.26   $151.25   $151.30  
  Purchase #2 $232.71   6.114%   $246.9379   $246.94   $246.95   $246.90  
  Purchase #3 $127.83   13.788%   $145.4552   $145.46   $145.45   $145.50  
  Purchase #4 $247.76   7.587%   $266.5576   $266.56   $266.55   $266.60  
  Purchase #5 $57.75   13.396%   $65.4862   $65.49   $65.50   $65.50  
  Purchase #6 $95.31   12.452%   $107.178   $107.18   $107.20   $107.20  
  Purchase #7 $236.75   11.251%   $263.3867   $263.39   $263.40   $263.40  
  7 purchase totals = $1,132.44       $1,246.2626   $1,246.28   $1,246.30   $1,246.40