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	$37.43	13.123%	$42.3419	$42.34	$42.35	$42.30
Purchase #2	$62.52	3.327%	$64.6	$64.60	$64.60	$64.60
Purchase #3	$66.81	6.251%	$70.9863	$70.99	$71.00	$71.00
Purchase #4	$40.54	6.377%	$43.1252	$43.13	$43.15	$43.10
Purchase #5	$34.94	7.701%	$37.6307	$37.63	$37.65	$37.60
Purchase #6	$68.43	3.505%	$70.8285	$70.83	$70.85	$70.80
Purchase #7	$113.82	13.373%	$129.0411	$129.04	$129.05	$129.00
7 purchase totals =	$424.49		$458.5537	$458.56	$458.65	$458.40