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	$33.78	12.699%	$38.0697	$38.07	$38.05	$38.10
Purchase #2	$159.68	7.814%	$172.1574	$172.16	$172.15	$172.20
Purchase #3	$125.84	11.598%	$140.4349	$140.43	$140.45	$140.40
Purchase #4	$153.89	7.582%	$165.5579	$165.56	$165.55	$165.60
Purchase #5	$101.38	5.444%	$106.8991	$106.90	$106.90	$106.90
Purchase #6	$76.74	8.275%	$83.0902	$83.09	$83.10	$83.10
Purchase #7	$167.76	12.446%	$188.6394	$188.64	$188.65	$188.60
7 purchase totals =	$819.07		$894.8486	$894.85	$894.85	$894.90