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 $85.54   13.718%   $97.2744   $97.27   $97.25   $97.30  
  Purchase #2 $195.98   11.815%   $219.135   $219.14   $219.15   $219.10  
  Purchase #3 $163.51   8.748%   $177.8139   $177.81   $177.80   $177.80  
  Purchase #4 $61.66   4.129%   $64.2059   $64.21   $64.20   $64.20  
  Purchase #5 $203.74   3.513%   $210.8974   $210.90   $210.90   $210.90  
  Purchase #6 $127.80   7.527%   $137.4195   $137.42   $137.40   $137.40  
  Purchase #7 $49.74   12.475%   $55.9451   $55.95   $55.95   $55.90  
  7 purchase totals = $887.97       $962.6912   $962.70   $962.65   $962.60