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 $220.60   7.770%   $237.7406   $237.74   $237.75   $237.70  
  Purchase #2 $243.83   8.465%   $264.4702   $264.47   $264.45   $264.50  
  Purchase #3 $110.56   8.191%   $119.616   $119.62   $119.60   $119.60  
  Purchase #4 $105.65   4.684%   $110.5986   $110.60   $110.60   $110.60  
  Purchase #5 $139.71   13.342%   $158.3501   $158.35   $158.35   $158.40  
  Purchase #6 $14.66   8.640%   $15.9266   $15.93   $15.95   $15.90  
  Purchase #7 $120.90   9.730%   $132.6636   $132.66   $132.65   $132.70  
  7 purchase totals = $955.91       $1,039.3657   $1,039.37   $1,039.35   $1,039.40