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 $118.75   6.611%   $126.6006   $126.60   $126.60   $126.60  
  Purchase #2 $189.71   4.756%   $198.7326   $198.73   $198.75   $198.70  
  Purchase #3 $154.54   12.430%   $173.7493   $173.75   $173.75   $173.70  
  Purchase #4 $207.41   6.165%   $220.1968   $220.20   $220.20   $220.20  
  Purchase #5 $140.35   10.725%   $155.4025   $155.40   $155.40   $155.40  
  Purchase #6 $99.88   6.141%   $106.0136   $106.01   $106.00   $106.00  
  Purchase #7 $185.44   7.636%   $199.6002   $199.60   $199.60   $199.60  
  7 purchase totals = $1,096.08       $1,180.2956   $1,180.29   $1,180.30   $1,180.20