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 $196.29   10.752%   $217.3951   $217.40   $217.40   $217.40  
  Purchase #2 $51.61   11.783%   $57.6912   $57.69   $57.70   $57.70  
  Purchase #3 $119.48   11.569%   $133.3026   $133.30   $133.30   $133.30  
  Purchase #4 $230.58   11.842%   $257.8853   $257.89   $257.90   $257.90  
  Purchase #5 $234.92   8.266%   $254.3385   $254.34   $254.35   $254.30  
  Purchase #6 $124.93   7.667%   $134.5084   $134.51   $134.50   $134.50  
  Purchase #7 $182.59   5.617%   $192.8461   $192.85   $192.85   $192.80  
  7 purchase totals = $1,140.40       $1,247.9672   $1,247.98   $1,248.00   $1,247.90