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 $242.28   5.242%   $254.9803   $254.98   $255.00   $255.00  
  Purchase #2 $89.74   5.414%   $94.5985   $94.60   $94.60   $94.60  
  Purchase #3 $72.94   6.567%   $77.73   $77.73   $77.75   $77.70  
  Purchase #4 $26.73   12.862%   $30.168   $30.17   $30.15   $30.20  
  Purchase #5 $72.34   4.361%   $75.4947   $75.49   $75.50   $75.50  
  Purchase #6 $221.25   11.630%   $246.9814   $246.98   $247.00   $247.00  
  Purchase #7 $196.49   9.855%   $215.8541   $215.85   $215.85   $215.90  
  7 purchase totals = $921.77       $995.8070   $995.80   $995.85   $995.90