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 $114.54   10.302%   $126.3399   $126.34   $126.35   $126.30  
  Purchase #2 $183.91   11.315%   $204.7194   $204.72   $204.70   $204.70  
  Purchase #3 $131.69   13.447%   $149.3984   $149.40   $149.40   $149.40  
  Purchase #4 $78.33   7.397%   $84.1241   $84.12   $84.10   $84.10  
  Purchase #5 $53.25   10.741%   $58.9696   $58.97   $58.95   $59.00  
  Purchase #6 $16.75   3.399%   $17.3193   $17.32   $17.30   $17.30  
  Purchase #7 $107.32   4.210%   $111.8382   $111.84   $111.85   $111.80  
  7 purchase totals = $685.79       $752.7089   $752.71   $752.65   $752.60