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 $59.97   12.686%   $67.5778   $67.58   $67.60   $67.60  
  Purchase #2 $250.62   10.665%   $277.3486   $277.35   $277.35   $277.30  
  Purchase #3 $70.83   5.186%   $74.5032   $74.50   $74.50   $74.50  
  Purchase #4 $14.67   12.720%   $16.536   $16.54   $16.55   $16.50  
  Purchase #5 $170.47   10.681%   $188.6779   $188.68   $188.70   $188.70  
  Purchase #6 $116.78   3.136%   $120.4422   $120.44   $120.45   $120.40  
  Purchase #7 $245.34   10.125%   $270.1807   $270.18   $270.20   $270.20  
  7 purchase totals = $928.68       $1,015.2664   $1,015.27   $1,015.35   $1,015.20