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 $241.80   8.267%   $261.7896   $261.79   $261.80   $261.80  
  Purchase #2 $36.33   8.637%   $39.4678   $39.47   $39.45   $39.50  
  Purchase #3 $92.50   12.628%   $104.1809   $104.18   $104.20   $104.20  
  Purchase #4 $150.70   4.507%   $157.492   $157.49   $157.50   $157.50  
  Purchase #5 $35.87   9.491%   $39.2744   $39.27   $39.25   $39.30  
  Purchase #6 $18.67   9.732%   $20.487   $20.49   $20.50   $20.50  
  Purchase #7 $131.90   5.820%   $139.5766   $139.58   $139.60   $139.60  
  7 purchase totals = $707.77       $762.2683   $762.27   $762.30   $762.40