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 $201.46   8.365%   $218.3121   $218.31   $218.30   $218.30  
  Purchase #2 $53.86   11.117%   $59.8476   $59.85   $59.85   $59.80  
  Purchase #3 $172.56   13.530%   $195.9074   $195.91   $195.90   $195.90  
  Purchase #4 $77.28   8.639%   $83.9562   $83.96   $83.95   $84.00  
  Purchase #5 $14.34   11.667%   $16.013   $16.01   $16.00   $16.00  
  Purchase #6 $46.29   3.652%   $47.9805   $47.98   $48.00   $48.00  
  Purchase #7 $214.32   3.638%   $222.117   $222.12   $222.10   $222.10  
  7 purchase totals = $780.11       $844.1338   $844.14   $844.10   $844.10