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 $192.27   6.344%   $204.4676   $204.47   $204.45   $204.50  
  Purchase #2 $203.60   12.427%   $228.9014   $228.90   $228.90   $228.90  
  Purchase #3 $151.27   5.371%   $159.3947   $159.39   $159.40   $159.40  
  Purchase #4 $217.26   13.183%   $245.9014   $245.90   $245.90   $245.90  
  Purchase #5 $54.98   10.508%   $60.7573   $60.76   $60.75   $60.80  
  Purchase #6 $19.88   9.111%   $21.6913   $21.69   $21.70   $21.70  
  Purchase #7 $128.35   6.284%   $136.4155   $136.42   $136.40   $136.40  
  7 purchase totals = $967.61       $1,057.5292   $1,057.53   $1,057.50   $1,057.60