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 $164.87   11.717%   $184.1878   $184.19   $184.20   $184.20  
  Purchase #2 $152.33   9.363%   $166.5927   $166.59   $166.60   $166.60  
  Purchase #3 $115.58   3.757%   $119.9223   $119.92   $119.90   $119.90  
  Purchase #4 $12.90   11.713%   $14.411   $14.41   $14.40   $14.40  
  Purchase #5 $217.93   3.570%   $225.7101   $225.71   $225.70   $225.70  
  Purchase #6 $139.91   9.630%   $153.3833   $153.38   $153.40   $153.40  
  Purchase #7 $118.67   11.622%   $132.4618   $132.46   $132.45   $132.50  
  7 purchase totals = $922.19       $996.6690   $996.66   $996.65   $996.70