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	$9.52	6.734%	$10.1611	$10.16	$10.15	$10.20
Purchase #2	$25.52	10.791%	$28.2739	$28.27	$28.25	$28.30
Purchase #3	$54.62	5.673%	$57.7186	$57.72	$57.70	$57.70
Purchase #4	$57.39	5.174%	$60.3594	$60.36	$60.35	$60.40
Purchase #5	$173.42	8.317%	$187.8433	$187.84	$187.85	$187.80
Purchase #6	$73.89	5.580%	$78.0131	$78.01	$78.00	$78.00
Purchase #7	$38.37	9.641%	$42.0693	$42.07	$42.05	$42.10
7 purchase totals =	$432.73		$464.4387	$464.43	$464.35	$464.50