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 $69.37   3.822%   $72.0213   $72.02   $72.00   $72.00  
  Purchase #2 $124.52   3.631%   $129.0413   $129.04   $129.05   $129.00  
  Purchase #3 $111.77   13.412%   $126.7606   $126.76   $126.75   $126.80  
  Purchase #4 $63.59   11.560%   $70.941   $70.94   $70.95   $70.90  
  Purchase #5 $93.76   11.330%   $104.383   $104.38   $104.40   $104.40  
  Purchase #6 $18.28   3.187%   $18.8626   $18.86   $18.85   $18.90  
  Purchase #7 $70.30   5.547%   $74.1995   $74.20   $74.20   $74.20  
  7 purchase totals = $551.59       $596.2093   $596.20   $596.20   $596.20