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 $116.93   7.706%   $125.9406   $125.94   $125.95   $125.90  
  Purchase #2 $6.41   7.181%   $6.8703   $6.87   $6.85   $6.90  
  Purchase #3 $104.78   11.801%   $117.1451   $117.15   $117.15   $117.10  
  Purchase #4 $60.57   8.364%   $65.6361   $65.64   $65.65   $65.60  
  Purchase #5 $237.84   3.802%   $246.8827   $246.88   $246.90   $246.90  
  Purchase #6 $204.86   5.115%   $215.3386   $215.34   $215.35   $215.30  
  Purchase #7 $25.78   5.466%   $27.1891   $27.19   $27.20   $27.20  
  7 purchase totals = $757.17       $805.0025   $805.01   $805.05   $804.90