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 $29.28   3.700%   $30.3634   $30.36   $30.35   $30.40  
  Purchase #2 $141.72   3.195%   $146.248   $146.25   $146.25   $146.20  
  Purchase #3 $161.62   13.297%   $183.1106   $183.11   $183.10   $183.10  
  Purchase #4 $32.72   5.548%   $34.5353   $34.54   $34.55   $34.50  
  Purchase #5 $59.47   5.639%   $62.8235   $62.82   $62.80   $62.80  
  Purchase #6 $53.69   7.132%   $57.5192   $57.52   $57.50   $57.50  
  Purchase #7 $198.29   10.575%   $219.2592   $219.26   $219.25   $219.30  
  7 purchase totals = $676.79       $733.8592   $733.86   $733.80   $733.80