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	$150.96	8.782%	$164.2173	$164.22	$164.20	$164.20
Purchase #2	$52.28	4.841%	$54.8109	$54.81	$54.80	$54.80
Purchase #3	$169.62	12.167%	$190.2577	$190.26	$190.25	$190.30
Purchase #4	$33.99	9.528%	$37.2286	$37.23	$37.25	$37.20
Purchase #5	$189.69	8.400%	$205.624	$205.62	$205.60	$205.60
Purchase #6	$108.42	13.681%	$123.2529	$123.25	$123.25	$123.30
Purchase #7	$157.83	8.624%	$171.4413	$171.44	$171.45	$171.40
7 purchase totals =	$862.79		$946.8327	$946.83	$946.80	$946.80