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 $113.95   4.751%   $119.3638   $119.36   $119.35   $119.40  
  Purchase #2 $203.38   11.274%   $226.3091   $226.31   $226.30   $226.30  
  Purchase #3 $195.43   11.201%   $217.3201   $217.32   $217.30   $217.30  
  Purchase #4 $194.26   6.717%   $207.3084   $207.31   $207.30   $207.30  
  Purchase #5 $48.28   5.491%   $50.9311   $50.93   $50.95   $50.90  
  Purchase #6 $54.95   5.819%   $58.1475   $58.15   $58.15   $58.10  
  Purchase #7 $72.57   9.796%   $79.679   $79.68   $79.70   $79.70  
  7 purchase totals = $882.82       $959.0590   $959.06   $959.05   $959.00