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 $187.57   13.163%   $212.2598   $212.26   $212.25   $212.30  
  Purchase #2 $114.26   9.431%   $125.0359   $125.04   $125.05   $125.00  
  Purchase #3 $71.39   10.332%   $78.766   $78.77   $78.75   $78.80  
  Purchase #4 $59.64   9.571%   $65.3481   $65.35   $65.35   $65.30  
  Purchase #5 $48.48   7.583%   $52.1562   $52.16   $52.15   $52.20  
  Purchase #6 $193.76   4.403%   $202.2913   $202.29   $202.30   $202.30  
  Purchase #7 $56.48   9.206%   $61.6795   $61.68   $61.70   $61.70  
  7 purchase totals = $731.58       $797.5368   $797.55   $797.55   $797.60