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	$106.56	11.595%	$118.9156	$118.92	$118.90	$118.90
Purchase #2	$131.37	11.407%	$146.3554	$146.36	$146.35	$146.40
Purchase #3	$59.92	9.294%	$65.489	$65.49	$65.50	$65.50
Purchase #4	$94.78	11.489%	$105.6693	$105.67	$105.65	$105.70
Purchase #5	$73.84	3.308%	$76.2826	$76.28	$76.30	$76.30
Purchase #6	$146.67	4.346%	$153.0443	$153.04	$153.05	$153.00
Purchase #7	$137.96	8.846%	$150.1639	$150.16	$150.15	$150.20
7 purchase totals =	$751.10		$815.9201	$815.92	$815.90	$816.00