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 $236.73   10.563%   $261.7358   $261.74   $261.75   $261.70  
  Purchase #2 $72.99   4.120%   $75.9972   $76.00   $76.00   $76.00  
  Purchase #3 $191.87   13.726%   $218.2061   $218.21   $218.20   $218.20  
  Purchase #4 $104.86   11.846%   $117.2817   $117.28   $117.30   $117.30  
  Purchase #5 $59.33   9.630%   $65.0435   $65.04   $65.05   $65.00  
  Purchase #6 $49.73   6.677%   $53.0505   $53.05   $53.05   $53.10  
  Purchase #7 $232.58   10.434%   $256.8474   $256.85   $256.85   $256.80  
  7 purchase totals = $948.09       $1,048.1622   $1,048.17   $1,048.20   $1,048.10