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	$170.32	8.797%	$185.3031	$185.30	$185.30	$185.30
Purchase #2	$238.48	11.844%	$266.7256	$266.73	$266.75	$266.70
Purchase #3	$179.91	13.162%	$203.5898	$203.59	$203.60	$203.60
Purchase #4	$244.83	10.335%	$270.1332	$270.13	$270.15	$270.10
Purchase #5	$66.58	8.532%	$72.2606	$72.26	$72.25	$72.30
Purchase #6	$46.76	13.780%	$53.2035	$53.20	$53.20	$53.20
Purchase #7	$232.72	13.786%	$264.8028	$264.80	$264.80	$264.80
7 purchase totals =	$1,179.60		$1,316.0186	$1,316.01	$1,316.05	$1,316.00