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 $246.75   11.477%   $275.0695   $275.07   $275.05   $275.10  
  Purchase #2 $64.70   4.673%   $67.7234   $67.72   $67.70   $67.70  
  Purchase #3 $128.61   6.234%   $136.6275   $136.63   $136.65   $136.60  
  Purchase #4 $153.55   3.821%   $159.4171   $159.42   $159.40   $159.40  
  Purchase #5 $68.49   6.602%   $73.0117   $73.01   $73.00   $73.00  
  Purchase #6 $194.77   10.489%   $215.1994   $215.20   $215.20   $215.20  
  Purchase #7 $75.76   3.329%   $78.2821   $78.28   $78.30   $78.30  
  7 purchase totals = $932.63       $1,005.3307   $1,005.33   $1,005.30   $1,005.30