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 $86.72   12.694%   $97.7282   $97.73   $97.75   $97.70  
  Purchase #2 $150.95   10.605%   $166.9582   $166.96   $166.95   $167.00  
  Purchase #3 $246.45   6.706%   $262.9769   $262.98   $263.00   $263.00  
  Purchase #4 $116.34   11.128%   $129.2863   $129.29   $129.30   $129.30  
  Purchase #5 $174.49   8.471%   $189.271   $189.27   $189.25   $189.30  
  Purchase #6 $227.49   4.381%   $237.4563   $237.46   $237.45   $237.50  
  Purchase #7 $25.95   8.494%   $28.1542   $28.15   $28.15   $28.20  
  7 purchase totals = $1,028.39       $1,111.8311   $1,111.84   $1,111.85   $1,112.00