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 $57.30   9.174%   $62.5567   $62.56   $62.55   $62.60  
  Purchase #2 $45.27   5.326%   $47.6811   $47.68   $47.70   $47.70  
  Purchase #3 $156.71   11.687%   $175.0247   $175.02   $175.00   $175.00  
  Purchase #4 $235.48   5.513%   $248.462   $248.46   $248.45   $248.50  
  Purchase #5 $35.31   13.321%   $40.0136   $40.01   $40.00   $40.00  
  Purchase #6 $118.54   3.172%   $122.3001   $122.30   $122.30   $122.30  
  Purchase #7 $99.61   11.312%   $110.8779   $110.88   $110.90   $110.90  
  7 purchase totals = $748.22       $806.9161   $806.91   $806.90   $807.00