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	$228.60	11.482%	$254.8479	$254.85	$254.85	$254.80
Purchase #2	$40.89	3.331%	$42.252	$42.25	$42.25	$42.30
Purchase #3	$107.73	6.554%	$114.7906	$114.79	$114.80	$114.80
Purchase #4	$227.56	5.293%	$239.6048	$239.60	$239.60	$239.60
Purchase #5	$66.69	5.592%	$70.4193	$70.42	$70.40	$70.40
Purchase #6	$53.40	13.688%	$60.7094	$60.71	$60.70	$60.70
Purchase #7	$90.99	5.388%	$95.8925	$95.89	$95.90	$95.90
7 purchase totals =	$815.86		$878.5165	$878.51	$878.50	$878.50