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	$34.89	7.756%	$37.5961	$37.60	$37.60	$37.60
Purchase #2	$35.79	12.642%	$40.3146	$40.31	$40.30	$40.30
Purchase #3	$77.71	8.832%	$84.5733	$84.57	$84.55	$84.60
Purchase #4	$161.52	4.533%	$168.8417	$168.84	$168.85	$168.80
Purchase #5	$228.28	6.764%	$243.7209	$243.72	$243.70	$243.70
Purchase #6	$33.82	12.543%	$38.062	$38.06	$38.05	$38.10
Purchase #7	$127.57	5.711%	$134.8555	$134.86	$134.85	$134.90
7 purchase totals =	$699.58		$747.9641	$747.96	$747.90	$748.00