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	$37.31	13.489%	$42.3427	$42.34	$42.35	$42.30
Purchase #2	$132.80	11.733%	$148.3814	$148.38	$148.40	$148.40
Purchase #3	$220.90	9.621%	$242.1528	$242.15	$242.15	$242.20
Purchase #4	$55.30	7.841%	$59.6361	$59.64	$59.65	$59.60
Purchase #5	$213.38	7.262%	$228.8757	$228.88	$228.90	$228.90
Purchase #6	$165.69	8.187%	$179.255	$179.26	$179.25	$179.30
Purchase #7	$50.88	4.388%	$53.1126	$53.11	$53.10	$53.10
7 purchase totals =	$876.26		$953.7563	$953.76	$953.80	$953.80