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	$182.43	10.115%	$200.8828	$200.88	$200.90	$200.90
Purchase #2	$247.93	6.591%	$264.2711	$264.27	$264.25	$264.30
Purchase #3	$48.53	10.542%	$53.646	$53.65	$53.65	$53.60
Purchase #4	$164.39	5.501%	$173.4331	$173.43	$173.45	$173.40
Purchase #5	$144.71	7.226%	$155.1667	$155.17	$155.15	$155.20
Purchase #6	$155.93	8.798%	$169.6487	$169.65	$169.65	$169.60
Purchase #7	$91.55	10.160%	$100.8515	$100.85	$100.85	$100.90
7 purchase totals =	$1,035.47		$1,117.8999	$1,117.90	$1,117.90	$1,117.90