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 $56.99   8.735%   $61.9681   $61.97   $61.95   $62.00  
  Purchase #2 $84.74   13.454%   $96.1409   $96.14   $96.15   $96.10  
  Purchase #3 $209.64   13.620%   $238.193   $238.19   $238.20   $238.20  
  Purchase #4 $37.61   10.357%   $41.5053   $41.51   $41.50   $41.50  
  Purchase #5 $157.74   8.343%   $170.9002   $170.90   $170.90   $170.90  
  Purchase #6 $221.45   8.493%   $240.2577   $240.26   $240.25   $240.30  
  Purchase #7 $42.62   7.419%   $45.782   $45.78   $45.80   $45.80  
  7 purchase totals = $810.79       $894.7472   $894.75   $894.75   $894.80