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	$99.35	12.365%	$111.6346	$111.63	$111.65	$111.60
Purchase #2	$30.35	4.122%	$31.601	$31.60	$31.60	$31.60
Purchase #3	$33.52	6.505%	$35.7005	$35.70	$35.70	$35.70
Purchase #4	$76.56	9.389%	$83.7482	$83.75	$83.75	$83.70
Purchase #5	$24.90	13.501%	$28.2617	$28.26	$28.25	$28.30
Purchase #6	$21.31	5.299%	$22.4392	$22.44	$22.45	$22.40
Purchase #7	$234.86	12.611%	$264.4782	$264.48	$264.50	$264.50
7 purchase totals =	$520.85		$577.8634	$577.86	$577.90	$577.80