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 $119.73   8.407%   $129.7957   $129.80   $129.80   $129.80  
  Purchase #2 $143.82   10.108%   $158.3573   $158.36   $158.35   $158.40  
  Purchase #3 $101.68   3.350%   $105.0863   $105.09   $105.10   $105.10  
  Purchase #4 $46.53   6.567%   $49.5856   $49.59   $49.60   $49.60  
  Purchase #5 $245.47   3.388%   $253.7865   $253.79   $253.80   $253.80  
  Purchase #6 $164.49   3.565%   $170.3541   $170.35   $170.35   $170.40  
  Purchase #7 $53.48   5.431%   $56.3845   $56.38   $56.40   $56.40  
  7 purchase totals = $875.20       $923.3500   $923.36   $923.40   $923.50