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 $62.38   13.160%   $70.5892   $70.59   $70.60   $70.60  
  Purchase #2 $225.43   9.667%   $247.2223   $247.22   $247.20   $247.20  
  Purchase #3 $38.49   12.427%   $43.2732   $43.27   $43.25   $43.30  
  Purchase #4 $176.65   3.591%   $182.9935   $182.99   $183.00   $183.00  
  Purchase #5 $9.46   9.586%   $10.3668   $10.37   $10.35   $10.40  
  Purchase #6 $139.90   13.785%   $159.1852   $159.19   $159.20   $159.20  
  Purchase #7 $217.57   5.501%   $229.5385   $229.54   $229.55   $229.50  
  7 purchase totals = $869.88       $943.1687   $943.17   $943.15   $943.20