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	$76.32	9.132%	$83.2895	$83.29	$83.30	$83.30
Purchase #2	$136.47	6.530%	$145.3815	$145.38	$145.40	$145.40
Purchase #3	$210.67	11.392%	$234.6695	$234.67	$234.65	$234.70
Purchase #4	$103.65	7.236%	$111.1501	$111.15	$111.15	$111.20
Purchase #5	$132.60	5.672%	$140.1211	$140.12	$140.10	$140.10
Purchase #6	$126.45	8.446%	$137.13	$137.13	$137.15	$137.10
Purchase #7	$98.27	11.308%	$109.3824	$109.38	$109.40	$109.40
7 purchase totals =	$884.43		$961.1241	$961.12	$961.15	$961.20