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	$15.51	12.829%	$17.4998	$17.50	$17.50	$17.50
Purchase #2	$232.74	11.330%	$259.1094	$259.11	$259.10	$259.10
Purchase #3	$211.42	5.160%	$222.3293	$222.33	$222.35	$222.30
Purchase #4	$122.70	6.846%	$131.1	$131.10	$131.10	$131.10
Purchase #5	$99.87	10.614%	$110.4702	$110.47	$110.45	$110.50
Purchase #6	$149.52	8.545%	$162.2965	$162.30	$162.30	$162.30
Purchase #7	$196.84	10.539%	$217.585	$217.59	$217.60	$217.60
7 purchase totals =	$1,028.60		$1,120.3902	$1,120.40	$1,120.40	$1,120.40