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	$61.94	5.706%	$65.4743	$65.47	$65.45	$65.50
Purchase #2	$183.64	3.528%	$190.1188	$190.12	$190.10	$190.10
Purchase #3	$105.72	4.500%	$110.4774	$110.48	$110.50	$110.50
Purchase #4	$81.61	7.697%	$87.8915	$87.89	$87.90	$87.90
Purchase #5	$121.39	8.640%	$131.8781	$131.88	$131.90	$131.90
Purchase #6	$155.54	11.375%	$173.2327	$173.23	$173.25	$173.20
Purchase #7	$68.63	12.613%	$77.2863	$77.29	$77.30	$77.30
7 purchase totals =	$778.47		$836.3591	$836.36	$836.40	$836.40