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 $95.45   8.671%   $103.7265   $103.73   $103.75   $103.70  
  Purchase #2 $242.71   13.557%   $275.6142   $275.61   $275.60   $275.60  
  Purchase #3 $6.35   13.420%   $7.2022   $7.20   $7.20   $7.20  
  Purchase #4 $214.61   13.706%   $244.0244   $244.02   $244.00   $244.00  
  Purchase #5 $232.69   10.666%   $257.5087   $257.51   $257.50   $257.50  
  Purchase #6 $222.91   6.532%   $237.4705   $237.47   $237.45   $237.50  
  Purchase #7 $173.92   12.552%   $195.7504   $195.75   $195.75   $195.80  
  7 purchase totals = $1,188.64       $1,321.2969   $1,321.29   $1,321.25   $1,321.30