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	$156.69	9.619%	$171.762	$171.76	$171.75	$171.80
Purchase #2	$104.42	9.784%	$114.6365	$114.64	$114.65	$114.60
Purchase #3	$141.53	13.119%	$160.0973	$160.10	$160.10	$160.10
Purchase #4	$33.74	5.281%	$35.5218	$35.52	$35.50	$35.50
Purchase #5	$132.99	9.122%	$145.1213	$145.12	$145.10	$145.10
Purchase #6	$96.77	8.694%	$105.1832	$105.18	$105.20	$105.20
Purchase #7	$59.33	3.640%	$61.4896	$61.49	$61.50	$61.50
7 purchase totals =	$725.47		$793.8117	$793.81	$793.80	$793.80