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	$159.27	8.818%	$173.3144	$173.31	$173.30	$173.30
Purchase #2	$86.81	5.716%	$91.7721	$91.77	$91.75	$91.80
Purchase #3	$250.72	12.740%	$282.6617	$282.66	$282.65	$282.70
Purchase #4	$205.61	13.339%	$233.0363	$233.04	$233.05	$233.00
Purchase #5	$35.93	7.655%	$38.6804	$38.68	$38.70	$38.70
Purchase #6	$40.50	12.642%	$45.62	$45.62	$45.60	$45.60
Purchase #7	$116.79	12.678%	$131.5966	$131.60	$131.60	$131.60
7 purchase totals =	$895.63		$996.6815	$996.68	$996.65	$996.70