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 $104.61   13.253%   $118.474   $118.47   $118.45   $118.50  
  Purchase #2 $168.34   9.809%   $184.8525   $184.85   $184.85   $184.90  
  Purchase #3 $90.53   8.156%   $97.9136   $97.91   $97.90   $97.90  
  Purchase #4 $158.29   7.645%   $170.3913   $170.39   $170.40   $170.40  
  Purchase #5 $195.51   7.289%   $209.7607   $209.76   $209.75   $209.80  
  Purchase #6 $129.85   3.398%   $134.2623   $134.26   $134.25   $134.30  
  Purchase #7 $125.78   7.241%   $134.8877   $134.89   $134.90   $134.90  
  7 purchase totals = $972.91       $1,050.5421   $1,050.53   $1,050.50   $1,050.70