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 $57.59   5.495%   $60.7546   $60.75   $60.75   $60.80  
  Purchase #2 $53.39   4.475%   $55.7792   $55.78   $55.80   $55.80  
  Purchase #3 $157.29   7.364%   $168.8728   $168.87   $168.85   $168.90  
  Purchase #4 $135.89   9.343%   $148.5862   $148.59   $148.60   $148.60  
  Purchase #5 $86.85   8.525%   $94.254   $94.25   $94.25   $94.30  
  Purchase #6 $197.66   9.450%   $216.3389   $216.34   $216.35   $216.30  
  Purchase #7 $51.49   11.133%   $57.2224   $57.22   $57.20   $57.20  
  7 purchase totals = $740.16       $801.8081   $801.80   $801.80   $801.90