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 $222.63   3.462%   $230.3375   $230.34   $230.35   $230.30  
  Purchase #2 $53.87   10.633%   $59.598   $59.60   $59.60   $59.60  
  Purchase #3 $78.28   4.865%   $82.0883   $82.09   $82.10   $82.10  
  Purchase #4 $87.68   6.764%   $93.6107   $93.61   $93.60   $93.60  
  Purchase #5 $37.78   5.757%   $39.955   $39.96   $39.95   $40.00  
  Purchase #6 $221.26   9.450%   $242.1691   $242.17   $242.15   $242.20  
  Purchase #7 $8.77   11.759%   $9.8013   $9.80   $9.80   $9.80  
  7 purchase totals = $710.27       $757.5599   $757.57   $757.55   $757.60