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 $43.42   11.681%   $48.4919   $48.49   $48.50   $48.50  
  Purchase #2 $225.67   8.400%   $244.6263   $244.63   $244.65   $244.60  
  Purchase #3 $114.78   4.560%   $120.014   $120.01   $120.00   $120.00  
  Purchase #4 $170.65   8.739%   $185.5631   $185.56   $185.55   $185.60  
  Purchase #5 $239.89   7.134%   $257.0038   $257.00   $257.00   $257.00  
  Purchase #6 $50.57   10.375%   $55.8166   $55.82   $55.80   $55.80  
  Purchase #7 $43.92   4.803%   $46.0295   $46.03   $46.05   $46.00  
  7 purchase totals = $888.90       $957.5452   $957.54   $957.55   $957.50