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 $43.49   12.527%   $48.938   $48.94   $48.95   $48.90  
  Purchase #2 $204.63   3.287%   $211.3562   $211.36   $211.35   $211.40  
  Purchase #3 $77.87   7.521%   $83.7266   $83.73   $83.75   $83.70  
  Purchase #4 $34.38   5.335%   $36.2142   $36.21   $36.20   $36.20  
  Purchase #5 $97.70   9.560%   $107.0401   $107.04   $107.05   $107.00  
  Purchase #6 $227.30   8.748%   $247.1842   $247.18   $247.20   $247.20  
  Purchase #7 $72.40   3.544%   $74.9659   $74.97   $74.95   $75.00  
  7 purchase totals = $757.77       $809.4252   $809.43   $809.45   $809.40