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	$211.91	4.362%	$221.1535	$221.15	$221.15	$221.20
Purchase #2	$86.50	4.281%	$90.2031	$90.20	$90.20	$90.20
Purchase #3	$36.89	11.437%	$41.1091	$41.11	$41.10	$41.10
Purchase #4	$210.35	7.834%	$226.8288	$226.83	$226.85	$226.80
Purchase #5	$129.45	6.351%	$137.6714	$137.67	$137.65	$137.70
Purchase #6	$78.47	13.763%	$89.2698	$89.27	$89.25	$89.30
Purchase #7	$17.93	8.309%	$19.4198	$19.42	$19.40	$19.40
7 purchase totals =	$771.50		$825.6555	$825.65	$825.60	$825.70