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 $68.73   12.106%   $77.0505   $77.05   $77.05   $77.10  
  Purchase #2 $228.41   9.322%   $249.7024   $249.70   $249.70   $249.70  
  Purchase #3 $123.92   6.492%   $131.9649   $131.96   $131.95   $132.00  
  Purchase #4 $58.45   10.433%   $64.5481   $64.55   $64.55   $64.50  
  Purchase #5 $159.82   12.389%   $179.6201   $179.62   $179.60   $179.60  
  Purchase #6 $168.38   13.446%   $191.0204   $191.02   $191.00   $191.00  
  Purchase #7 $59.90   3.297%   $61.8749   $61.87   $61.85   $61.90  
  7 purchase totals = $867.61       $955.7813   $955.77   $955.70   $955.80