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 $92.95   12.460%   $104.5316   $104.53   $104.55   $104.50  
  Purchase #2 $205.84   11.511%   $229.5342   $229.53   $229.55   $229.50  
  Purchase #3 $58.32   11.156%   $64.8262   $64.83   $64.85   $64.80  
  Purchase #4 $118.36   5.113%   $124.4117   $124.41   $124.40   $124.40  
  Purchase #5 $193.60   11.846%   $216.5339   $216.53   $216.55   $216.50  
  Purchase #6 $151.98   4.306%   $158.5243   $158.52   $158.50   $158.50  
  Purchase #7 $16.25   4.259%   $16.9421   $16.94   $16.95   $16.90  
  7 purchase totals = $837.30       $915.3040   $915.29   $915.35   $915.10