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 $116.94   8.517%   $126.8998   $126.90   $126.90   $126.90  
  Purchase #2 $127.43   12.771%   $143.7041   $143.70   $143.70   $143.70  
  Purchase #3 $159.34   6.286%   $169.3561   $169.36   $169.35   $169.40  
  Purchase #4 $88.97   10.456%   $98.2727   $98.27   $98.25   $98.30  
  Purchase #5 $230.49   5.375%   $242.8788   $242.88   $242.90   $242.90  
  Purchase #6 $78.36   12.144%   $87.876   $87.88   $87.90   $87.90  
  Purchase #7 $98.57   5.419%   $103.9115   $103.91   $103.90   $103.90  
  7 purchase totals = $900.10       $972.8990   $972.90   $972.90   $973.00