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	$123.74	3.371%	$127.9113	$127.91	$127.90	$127.90
Purchase #2	$153.53	10.798%	$170.1082	$170.11	$170.10	$170.10
Purchase #3	$230.75	7.252%	$247.484	$247.48	$247.50	$247.50
Purchase #4	$79.96	8.318%	$86.6111	$86.61	$86.60	$86.60
Purchase #5	$54.53	8.430%	$59.1269	$59.13	$59.15	$59.10
Purchase #6	$138.62	13.251%	$156.9885	$156.99	$157.00	$157.00
Purchase #7	$225.31	3.430%	$233.0381	$233.04	$233.05	$233.00
7 purchase totals =	$1,006.44		$1,081.2681	$1,081.27	$1,081.30	$1,081.20