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	$140.61	13.490%	$159.5783	$159.58	$159.60	$159.60
Purchase #2	$213.76	10.532%	$236.2732	$236.27	$236.25	$236.30
Purchase #3	$101.57	10.341%	$112.0734	$112.07	$112.05	$112.10
Purchase #4	$71.67	11.323%	$79.7852	$79.79	$79.80	$79.80
Purchase #5	$80.29	4.123%	$83.6004	$83.60	$83.60	$83.60
Purchase #6	$99.98	5.162%	$105.141	$105.14	$105.15	$105.10
Purchase #7	$147.97	8.540%	$160.6066	$160.61	$160.60	$160.60
7 purchase totals =	$855.85		$937.0581	$937.06	$937.05	$937.10