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 $213.71   6.848%   $228.3449   $228.34   $228.35   $228.30  
  Purchase #2 $50.82   5.629%   $53.6807   $53.68   $53.70   $53.70  
  Purchase #3 $233.69   8.578%   $253.7359   $253.74   $253.75   $253.70  
  Purchase #4 $57.60   11.780%   $64.3853   $64.39   $64.40   $64.40  
  Purchase #5 $94.73   8.574%   $102.8522   $102.85   $102.85   $102.90  
  Purchase #6 $204.41   5.255%   $215.1517   $215.15   $215.15   $215.20  
  Purchase #7 $47.66   12.633%   $53.6809   $53.68   $53.70   $53.70  
  7 purchase totals = $902.62       $971.8316   $971.83   $971.90   $971.90