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 $242.82   3.873%   $252.2244   $252.22   $252.20   $252.20  
  Purchase #2 $9.67   6.818%   $10.3293   $10.33   $10.35   $10.30  
  Purchase #3 $223.43   6.234%   $237.3586   $237.36   $237.35   $237.40  
  Purchase #4 $162.90   6.728%   $173.8599   $173.86   $173.85   $173.90  
  Purchase #5 $168.73   4.538%   $176.387   $176.39   $176.40   $176.40  
  Purchase #6 $43.37   5.302%   $45.6695   $45.67   $45.65   $45.70  
  Purchase #7 $217.43   4.770%   $227.8014   $227.80   $227.80   $227.80  
  7 purchase totals = $1,068.35       $1,123.6301   $1,123.63   $1,123.60   $1,123.70