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 $33.62   11.866%   $37.6093   $37.61   $37.60   $37.60  
  Purchase #2 $244.59   8.429%   $265.2065   $265.21   $265.20   $265.20  
  Purchase #3 $243.43   7.512%   $261.7165   $261.72   $261.70   $261.70  
  Purchase #4 $51.80   7.243%   $55.5519   $55.55   $55.55   $55.60  
  Purchase #5 $98.98   5.268%   $104.1943   $104.19   $104.20   $104.20  
  Purchase #6 $22.61   9.865%   $24.8405   $24.84   $24.85   $24.80  
  Purchase #7 $24.91   9.133%   $27.185   $27.19   $27.20   $27.20  
  7 purchase totals = $719.94       $776.3040   $776.31   $776.30   $776.30