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	$32.64	3.634%	$33.8261	$33.83	$33.85	$33.80
Purchase #2	$172.73	11.660%	$192.8703	$192.87	$192.85	$192.90
Purchase #3	$16.65	8.862%	$18.1255	$18.13	$18.15	$18.10
Purchase #4	$106.41	3.146%	$109.7577	$109.76	$109.75	$109.80
Purchase #5	$177.25	13.692%	$201.5191	$201.52	$201.50	$201.50
Purchase #6	$245.87	13.582%	$279.2641	$279.26	$279.25	$279.30
Purchase #7	$38.28	4.685%	$40.0734	$40.07	$40.05	$40.10
7 purchase totals =	$789.83		$875.4362	$875.44	$875.40	$875.50