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 $66.68   5.195%   $70.144   $70.14   $70.15   $70.10  
  Purchase #2 $247.86   5.401%   $261.2469   $261.25   $261.25   $261.20  
  Purchase #3 $120.48   9.131%   $131.481   $131.48   $131.50   $131.50  
  Purchase #4 $47.49   11.843%   $53.1142   $53.11   $53.10   $53.10  
  Purchase #5 $240.43   11.197%   $267.3509   $267.35   $267.35   $267.40  
  Purchase #6 $244.63   8.408%   $265.1985   $265.20   $265.20   $265.20  
  Purchase #7 $234.58   10.714%   $259.7129   $259.71   $259.70   $259.70  
  7 purchase totals = $1,202.15       $1,308.2484   $1,308.24   $1,308.25   $1,308.20