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	$48.82	9.596%	$53.5048	$53.50	$53.50	$53.50
Purchase #2	$32.87	8.560%	$35.6837	$35.68	$35.70	$35.70
Purchase #3	$165.29	9.272%	$180.6157	$180.62	$180.60	$180.60
Purchase #4	$146.42	4.687%	$153.2827	$153.28	$153.30	$153.30
Purchase #5	$248.74	12.680%	$280.2802	$280.28	$280.30	$280.30
Purchase #6	$128.91	7.146%	$138.1219	$138.12	$138.10	$138.10
Purchase #7	$210.62	13.281%	$238.5924	$238.59	$238.60	$238.60
7 purchase totals =	$981.67		$1,080.0814	$1,080.07	$1,080.10	$1,080.10