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	$140.32	4.314%	$146.3734	$146.37	$146.35	$146.40
Purchase #2	$56.50	4.658%	$59.1318	$59.13	$59.15	$59.10
Purchase #3	$10.58	3.526%	$10.9531	$10.95	$10.95	$11.00
Purchase #4	$72.65	10.413%	$80.215	$80.22	$80.20	$80.20
Purchase #5	$67.50	11.140%	$75.0195	$75.02	$75.00	$75.00
Purchase #6	$210.37	5.344%	$221.6122	$221.61	$221.60	$221.60
Purchase #7	$22.97	12.515%	$25.8447	$25.84	$25.85	$25.80
7 purchase totals =	$580.89		$619.1497	$619.14	$619.10	$619.10