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 $62.72   8.777%   $68.2249   $68.22   $68.20   $68.20  
  Purchase #2 $139.97   12.374%   $157.2899   $157.29   $157.30   $157.30  
  Purchase #3 $121.31   4.427%   $126.6804   $126.68   $126.70   $126.70  
  Purchase #4 $156.25   3.650%   $161.9531   $161.95   $161.95   $162.00  
  Purchase #5 $156.53   3.306%   $161.7049   $161.70   $161.70   $161.70  
  Purchase #6 $240.58   6.536%   $256.3043   $256.30   $256.30   $256.30  
  Purchase #7 $59.56   9.334%   $65.1193   $65.12   $65.10   $65.10  
  7 purchase totals = $936.92       $997.2768   $997.26   $997.25   $997.30