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 $117.53   5.702%   $124.2316   $124.23   $124.25   $124.20  
  Purchase #2 $67.40   8.795%   $73.3278   $73.33   $73.35   $73.30  
  Purchase #3 $67.46   11.184%   $75.0047   $75.00   $75.00   $75.00  
  Purchase #4 $150.82   11.672%   $168.4237   $168.42   $168.40   $168.40  
  Purchase #5 $21.32   13.480%   $24.1939   $24.19   $24.20   $24.20  
  Purchase #6 $206.37   4.592%   $215.8465   $215.85   $215.85   $215.80  
  Purchase #7 $95.34   9.802%   $104.6852   $104.69   $104.70   $104.70  
  7 purchase totals = $726.24       $785.7134   $785.71   $785.75   $785.60