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	$138.89	9.664%	$152.3123	$152.31	$152.30	$152.30
Purchase #2	$90.32	4.430%	$94.3212	$94.32	$94.30	$94.30
Purchase #3	$9.98	3.333%	$10.3126	$10.31	$10.30	$10.30
Purchase #4	$48.52	3.588%	$50.2609	$50.26	$50.25	$50.30
Purchase #5	$136.72	10.813%	$151.5035	$151.50	$151.50	$151.50
Purchase #6	$246.87	6.302%	$262.4277	$262.43	$262.45	$262.40
Purchase #7	$93.61	9.108%	$102.136	$102.14	$102.15	$102.10
7 purchase totals =	$764.91		$823.2742	$823.27	$823.25	$823.20