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	$156.81	10.145%	$172.7184	$172.72	$172.70	$172.70
Purchase #2	$123.85	13.753%	$140.8831	$140.88	$140.90	$140.90
Purchase #3	$249.91	9.429%	$273.474	$273.47	$273.45	$273.50
Purchase #4	$222.58	3.118%	$229.52	$229.52	$229.50	$229.50
Purchase #5	$32.82	7.384%	$35.2434	$35.24	$35.25	$35.20
Purchase #6	$90.27	9.718%	$99.0424	$99.04	$99.05	$99.00
Purchase #7	$9.26	8.360%	$10.0341	$10.03	$10.05	$10.00
7 purchase totals =	$885.50		$960.9154	$960.90	$960.90	$960.80