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 $59.79   6.310%   $63.5627   $63.56   $63.55   $63.60  
  Purchase #2 $93.51   4.359%   $97.5861   $97.59   $97.60   $97.60  
  Purchase #3 $200.72   3.597%   $207.9399   $207.94   $207.95   $207.90  
  Purchase #4 $72.95   9.409%   $79.8139   $79.81   $79.80   $79.80  
  Purchase #5 $54.65   12.235%   $61.3364   $61.34   $61.35   $61.30  
  Purchase #6 $12.46   7.823%   $13.4347   $13.43   $13.45   $13.40  
  Purchase #7 $59.62   8.605%   $64.7503   $64.75   $64.75   $64.80  
  7 purchase totals = $553.70       $588.4240   $588.42   $588.45   $588.40