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 $42.34   11.733%   $47.3078   $47.31   $47.30   $47.30  
  Purchase #2 $101.98   11.847%   $114.0616   $114.06   $114.05   $114.10  
  Purchase #3 $165.43   13.356%   $187.5248   $187.52   $187.50   $187.50  
  Purchase #4 $61.66   11.745%   $68.902   $68.90   $68.90   $68.90  
  Purchase #5 $210.33   4.568%   $219.9379   $219.94   $219.95   $219.90  
  Purchase #6 $108.67   8.165%   $117.5429   $117.54   $117.55   $117.50  
  Purchase #7 $171.81   10.298%   $189.503   $189.50   $189.50   $189.50  
  7 purchase totals = $862.22       $944.7800   $944.77   $944.75   $944.70