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 $46.61   10.767%   $51.6285   $51.63   $51.65   $51.60  
  Purchase #2 $211.60   8.658%   $229.9203   $229.92   $229.90   $229.90  
  Purchase #3 $80.63   10.622%   $89.1945   $89.19   $89.20   $89.20  
  Purchase #4 $89.25   10.830%   $98.9158   $98.92   $98.90   $98.90  
  Purchase #5 $222.68   4.354%   $232.3755   $232.38   $232.40   $232.40  
  Purchase #6 $53.59   5.623%   $56.6034   $56.60   $56.60   $56.60  
  Purchase #7 $69.44   10.475%   $76.7138   $76.71   $76.70   $76.70  
  7 purchase totals = $773.80       $835.3518   $835.35   $835.35   $835.30