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	$210.82	12.797%	$237.7986	$237.80	$237.80	$237.80
Purchase #2	$70.82	11.391%	$78.8871	$78.89	$78.90	$78.90
Purchase #3	$39.42	4.560%	$41.2176	$41.22	$41.20	$41.20
Purchase #4	$106.74	6.209%	$113.3675	$113.37	$113.35	$113.40
Purchase #5	$77.58	13.771%	$88.2635	$88.26	$88.25	$88.30
Purchase #6	$142.47	9.377%	$155.8294	$155.83	$155.85	$155.80
Purchase #7	$122.87	7.117%	$131.6147	$131.61	$131.60	$131.60
7 purchase totals =	$770.72		$846.9784	$846.98	$846.95	$847.00