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 $104.68   8.703%   $113.7903   $113.79   $113.80   $113.80  
  Purchase #2 $209.48   7.607%   $225.4151   $225.42   $225.40   $225.40  
  Purchase #3 $35.50   7.425%   $38.1359   $38.14   $38.15   $38.10  
  Purchase #4 $76.46   6.369%   $81.3297   $81.33   $81.35   $81.30  
  Purchase #5 $149.93   7.116%   $160.599   $160.60   $160.60   $160.60  
  Purchase #6 $136.97   10.568%   $151.445   $151.45   $151.45   $151.40  
  Purchase #7 $160.92   5.104%   $169.1334   $169.13   $169.15   $169.10  
  7 purchase totals = $873.94       $939.8484   $939.86   $939.90   $939.70