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 $112.49   10.711%   $124.5388   $124.54   $124.55   $124.50  
  Purchase #2 $68.41   12.165%   $76.7321   $76.73   $76.75   $76.70  
  Purchase #3 $87.88   6.528%   $93.6168   $93.62   $93.60   $93.60  
  Purchase #4 $150.93   7.104%   $161.6521   $161.65   $161.65   $161.70  
  Purchase #5 $75.90   4.127%   $79.0324   $79.03   $79.05   $79.00  
  Purchase #6 $77.37   6.219%   $82.1816   $82.18   $82.20   $82.20  
  Purchase #7 $236.63   12.503%   $266.2158   $266.22   $266.20   $266.20  
  7 purchase totals = $809.61       $883.9696   $883.97   $884.00   $883.90