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 $174.56   12.871%   $197.0276   $197.03   $197.05   $197.00  
  Purchase #2 $85.25   9.491%   $93.3411   $93.34   $93.35   $93.30  
  Purchase #3 $160.50   7.799%   $173.0174   $173.02   $173.00   $173.00  
  Purchase #4 $116.63   6.126%   $123.7748   $123.77   $123.75   $123.80  
  Purchase #5 $160.76   13.543%   $182.5317   $182.53   $182.55   $182.50  
  Purchase #6 $154.44   10.232%   $170.2423   $170.24   $170.25   $170.20  
  Purchase #7 $118.91   5.715%   $125.7057   $125.71   $125.70   $125.70  
  7 purchase totals = $971.05       $1,065.6406   $1,065.64   $1,065.65   $1,065.50