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 $141.99   6.752%   $151.5772   $151.58   $151.60   $151.60  
  Purchase #2 $170.86   12.636%   $192.4499   $192.45   $192.45   $192.40  
  Purchase #3 $244.67   12.325%   $274.8256   $274.83   $274.85   $274.80  
  Purchase #4 $137.73   7.254%   $147.7209   $147.72   $147.70   $147.70  
  Purchase #5 $199.79   7.266%   $214.3067   $214.31   $214.30   $214.30  
  Purchase #6 $129.56   5.643%   $136.8711   $136.87   $136.85   $136.90  
  Purchase #7 $122.57   6.465%   $130.4942   $130.49   $130.50   $130.50  
  7 purchase totals = $1,147.17       $1,248.2456   $1,248.25   $1,248.25   $1,248.20