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 $22.57   10.845%   $25.0177   $25.02   $25.00   $25.00  
  Purchase #2 $5.53   5.678%   $5.844   $5.84   $5.85   $5.80  
  Purchase #3 $208.74   13.444%   $236.803   $236.80   $236.80   $236.80  
  Purchase #4 $29.71   12.151%   $33.3201   $33.32   $33.30   $33.30  
  Purchase #5 $25.36   10.694%   $28.072   $28.07   $28.05   $28.10  
  Purchase #6 $23.90   8.424%   $25.9133   $25.91   $25.90   $25.90  
  Purchase #7 $39.98   7.189%   $42.8542   $42.85   $42.85   $42.90  
  7 purchase totals = $355.79       $397.8243   $397.81   $397.75   $397.80