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	$99.79	11.376%	$111.1421	$111.14	$111.15	$111.10
Purchase #2	$120.98	6.750%	$129.1462	$129.15	$129.15	$129.10
Purchase #3	$148.32	11.701%	$165.6749	$165.67	$165.65	$165.70
Purchase #4	$34.60	11.431%	$38.5551	$38.56	$38.55	$38.60
Purchase #5	$26.98	4.379%	$28.1615	$28.16	$28.15	$28.20
Purchase #6	$37.54	13.316%	$42.5388	$42.54	$42.55	$42.50
Purchase #7	$133.86	5.472%	$141.1848	$141.18	$141.20	$141.20
7 purchase totals =	$602.07		$656.4034	$656.40	$656.40	$656.40