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	$159.60	9.199%	$174.2816	$174.28	$174.30	$174.30
Purchase #2	$50.89	3.722%	$52.7841	$52.78	$52.80	$52.80
Purchase #3	$118.74	4.294%	$123.8387	$123.84	$123.85	$123.80
Purchase #4	$205.88	8.658%	$223.7051	$223.71	$223.70	$223.70
Purchase #5	$157.73	9.232%	$172.2916	$172.29	$172.30	$172.30
Purchase #6	$49.81	11.410%	$55.4933	$55.49	$55.50	$55.50
Purchase #7	$53.35	12.614%	$60.0796	$60.08	$60.10	$60.10
7 purchase totals =	$796.00		$862.4740	$862.47	$862.55	$862.50