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	$35.32	12.166%	$39.617	$39.62	$39.60	$39.60
Purchase #2	$93.84	9.195%	$102.4686	$102.47	$102.45	$102.50
Purchase #3	$215.91	8.222%	$233.6621	$233.66	$233.65	$233.70
Purchase #4	$38.30	13.690%	$43.5433	$43.54	$43.55	$43.50
Purchase #5	$119.64	12.649%	$134.7733	$134.77	$134.75	$134.80
Purchase #6	$231.92	10.761%	$256.8769	$256.88	$256.90	$256.90
Purchase #7	$91.63	12.513%	$103.0957	$103.10	$103.10	$103.10
7 purchase totals =	$826.56		$914.0369	$914.04	$914.00	$914.10