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 $86.68   13.631%   $98.4954   $98.50   $98.50   $98.50  
  Purchase #2 $190.43   12.761%   $214.7308   $214.73   $214.75   $214.70  
  Purchase #3 $241.30   11.417%   $268.8492   $268.85   $268.85   $268.80  
  Purchase #4 $166.87   9.577%   $182.8511   $182.85   $182.85   $182.90  
  Purchase #5 $200.80   10.333%   $221.5487   $221.55   $221.55   $221.50  
  Purchase #6 $60.32   9.743%   $66.197   $66.20   $66.20   $66.20  
  Purchase #7 $236.55   13.172%   $267.7084   $267.71   $267.70   $267.70  
  7 purchase totals = $1,182.95       $1,320.3806   $1,320.39   $1,320.40   $1,320.30