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 $244.97   4.756%   $256.6208   $256.62   $256.60   $256.60  
  Purchase #2 $123.96   12.705%   $139.7091   $139.71   $139.70   $139.70  
  Purchase #3 $96.29   9.359%   $105.3018   $105.30   $105.30   $105.30  
  Purchase #4 $237.99   4.806%   $249.4278   $249.43   $249.45   $249.40  
  Purchase #5 $173.35   5.337%   $182.6017   $182.60   $182.60   $182.60  
  Purchase #6 $25.76   13.350%   $29.199   $29.20   $29.20   $29.20  
  Purchase #7 $196.77   11.643%   $219.6799   $219.68   $219.70   $219.70  
  7 purchase totals = $1,099.09       $1,182.5401   $1,182.54   $1,182.55   $1,182.50