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 $60.31   10.471%   $66.6251   $66.63   $66.65   $66.60  
  Purchase #2 $23.67   10.612%   $26.1819   $26.18   $26.20   $26.20  
  Purchase #3 $124.59   5.477%   $131.4138   $131.41   $131.40   $131.40  
  Purchase #4 $8.49   10.201%   $9.3561   $9.36   $9.35   $9.40  
  Purchase #5 $94.44   8.515%   $102.4816   $102.48   $102.50   $102.50  
  Purchase #6 $53.36   8.484%   $57.8871   $57.89   $57.90   $57.90  
  Purchase #7 $24.78   4.404%   $25.8713   $25.87   $25.85   $25.90  
  7 purchase totals = $389.64       $419.8169   $419.82   $419.85   $419.90