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 $61.38   7.449%   $65.9522   $65.95   $65.95   $66.00  
  Purchase #2 $39.54   9.708%   $43.3785   $43.38   $43.40   $43.40  
  Purchase #3 $235.60   10.495%   $260.3262   $260.33   $260.35   $260.30  
  Purchase #4 $153.58   3.380%   $158.771   $158.77   $158.75   $158.80  
  Purchase #5 $104.57   5.580%   $110.405   $110.41   $110.40   $110.40  
  Purchase #6 $100.39   12.303%   $112.741   $112.74   $112.75   $112.70  
  Purchase #7 $114.36   3.539%   $118.4072   $118.41   $118.40   $118.40  
  7 purchase totals = $809.42       $869.9811   $869.99   $870.00   $870.00