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 $60.43   6.526%   $64.3737   $64.37   $64.35   $64.40  
  Purchase #2 $234.79   13.243%   $265.8832   $265.88   $265.90   $265.90  
  Purchase #3 $70.50   7.177%   $75.5598   $75.56   $75.55   $75.60  
  Purchase #4 $103.97   9.266%   $113.6039   $113.60   $113.60   $113.60  
  Purchase #5 $165.74   13.534%   $188.1713   $188.17   $188.15   $188.20  
  Purchase #6 $146.69   12.290%   $164.7182   $164.72   $164.70   $164.70  
  Purchase #7 $112.52   5.696%   $118.9291   $118.93   $118.95   $118.90  
  7 purchase totals = $894.64       $991.2392   $991.23   $991.20   $991.30