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 $229.73   10.721%   $254.3594   $254.36   $254.35   $254.40  
  Purchase #2 $87.35   5.267%   $91.9507   $91.95   $91.95   $92.00  
  Purchase #3 $5.64   10.378%   $6.2253   $6.23   $6.25   $6.20  
  Purchase #4 $180.45   13.497%   $204.8053   $204.81   $204.80   $204.80  
  Purchase #5 $123.46   10.728%   $136.7048   $136.70   $136.70   $136.70  
  Purchase #6 $95.42   9.652%   $104.6299   $104.63   $104.65   $104.60  
  Purchase #7 $215.71   12.709%   $243.1246   $243.12   $243.10   $243.10  
  7 purchase totals = $937.76       $1,041.8000   $1,041.80   $1,041.80   $1,041.80