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 $244.87   4.434%   $255.7275   $255.73   $255.75   $255.70  
  Purchase #2 $125.57   12.194%   $140.882   $140.88   $140.90   $140.90  
  Purchase #3 $218.83   8.133%   $236.6274   $236.63   $236.65   $236.60  
  Purchase #4 $61.30   7.604%   $65.9613   $65.96   $65.95   $66.00  
  Purchase #5 $9.39   8.339%   $10.173   $10.17   $10.15   $10.20  
  Purchase #6 $201.85   7.323%   $216.6315   $216.63   $216.65   $216.60  
  Purchase #7 $58.70   6.644%   $62.6   $62.60   $62.60   $62.60  
  7 purchase totals = $920.51       $988.6027   $988.60   $988.65   $988.60