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	$233.45	8.383%	$253.0201	$253.02	$253.00	$253.00
Purchase #2	$79.64	13.474%	$90.3707	$90.37	$90.35	$90.40
Purchase #3	$116.43	7.178%	$124.7873	$124.79	$124.80	$124.80
Purchase #4	$231.47	12.678%	$260.8158	$260.82	$260.80	$260.80
Purchase #5	$166.79	4.274%	$173.9186	$173.92	$173.90	$173.90
Purchase #6	$23.56	10.118%	$25.9438	$25.94	$25.95	$25.90
Purchase #7	$12.73	5.753%	$13.4624	$13.46	$13.45	$13.50
7 purchase totals =	$864.07		$942.3187	$942.32	$942.25	$942.30