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 $64.61   12.706%   $72.8193   $72.82   $72.80   $72.80  
  Purchase #2 $238.60   12.664%   $268.8163   $268.82   $268.80   $268.80  
  Purchase #3 $204.94   6.277%   $217.8041   $217.80   $217.80   $217.80  
  Purchase #4 $97.74   8.725%   $106.2678   $106.27   $106.25   $106.30  
  Purchase #5 $177.85   9.604%   $194.9307   $194.93   $194.95   $194.90  
  Purchase #6 $72.87   12.444%   $81.9379   $81.94   $81.95   $81.90  
  Purchase #7 $125.99   12.385%   $141.5939   $141.59   $141.60   $141.60  
  7 purchase totals = $982.60       $1,084.1700   $1,084.17   $1,084.15   $1,084.10