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 $60.73   12.694%   $68.4391   $68.44   $68.45   $68.40  
  Purchase #2 $123.42   7.770%   $133.0097   $133.01   $133.00   $133.00  
  Purchase #3 $122.88   11.750%   $137.3184   $137.32   $137.30   $137.30  
  Purchase #4 $130.47   8.487%   $141.543   $141.54   $141.55   $141.50  
  Purchase #5 $51.75   13.170%   $58.5655   $58.57   $58.55   $58.60  
  Purchase #6 $197.44   3.538%   $204.4254   $204.43   $204.45   $204.40  
  Purchase #7 $177.33   3.131%   $182.8822   $182.88   $182.90   $182.90  
  7 purchase totals = $864.02       $926.1833   $926.19   $926.20   $926.10