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	$11.76	6.182%	$12.487	$12.49	$12.50	$12.50
Purchase #2	$94.66	11.393%	$105.4446	$105.44	$105.45	$105.40
Purchase #3	$88.29	13.840%	$100.5093	$100.51	$100.50	$100.50
Purchase #4	$138.33	7.799%	$149.1184	$149.12	$149.10	$149.10
Purchase #5	$192.33	10.219%	$211.9842	$211.98	$212.00	$212.00
Purchase #6	$226.40	13.353%	$256.6312	$256.63	$256.65	$256.60
Purchase #7	$227.36	8.262%	$246.1445	$246.14	$246.15	$246.10
7 purchase totals =	$979.13		$1,082.3192	$1,082.31	$1,082.35	$1,082.20