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	$123.26	11.776%	$137.7751	$137.78	$137.80	$137.80
Purchase #2	$134.44	11.733%	$150.2138	$150.21	$150.20	$150.20
Purchase #3	$48.75	3.168%	$50.2944	$50.29	$50.30	$50.30
Purchase #4	$161.79	11.345%	$180.1451	$180.15	$180.15	$180.10
Purchase #5	$54.50	9.487%	$59.6704	$59.67	$59.65	$59.70
Purchase #6	$49.39	6.805%	$52.751	$52.75	$52.75	$52.80
Purchase #7	$105.99	3.377%	$109.5693	$109.57	$109.55	$109.60
7 purchase totals =	$678.12		$740.4191	$740.42	$740.40	$740.50