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	$99.99	5.335%	$105.3245	$105.32	$105.30	$105.30
Purchase #2	$149.90	5.679%	$158.4128	$158.41	$158.40	$158.40
Purchase #3	$158.36	4.463%	$165.4276	$165.43	$165.45	$165.40
Purchase #4	$40.95	13.788%	$46.5962	$46.60	$46.60	$46.60
Purchase #5	$206.89	11.709%	$231.1148	$231.11	$231.10	$231.10
Purchase #6	$70.85	3.375%	$73.2412	$73.24	$73.25	$73.20
Purchase #7	$137.65	5.448%	$145.1492	$145.15	$145.15	$145.10
7 purchase totals =	$864.59		$925.2663	$925.26	$925.25	$925.10