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 $196.93   8.294%   $213.2634   $213.26   $213.25   $213.30  
  Purchase #2 $216.57   11.216%   $240.8605   $240.86   $240.85   $240.90  
  Purchase #3 $60.50   4.515%   $63.2316   $63.23   $63.25   $63.20  
  Purchase #4 $215.92   9.806%   $237.0931   $237.09   $237.10   $237.10  
  Purchase #5 $127.54   3.775%   $132.3546   $132.35   $132.35   $132.40  
  Purchase #6 $167.60   5.186%   $176.2917   $176.29   $176.30   $176.30  
  Purchase #7 $53.97   10.871%   $59.8371   $59.84   $59.85   $59.80  
  7 purchase totals = $1,039.03       $1,122.9320   $1,122.92   $1,122.95   $1,123.00