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	$89.29	12.350%	$100.3173	$100.32	$100.30	$100.30
Purchase #2	$38.73	9.602%	$42.4489	$42.45	$42.45	$42.40
Purchase #3	$176.77	4.573%	$184.8537	$184.85	$184.85	$184.90
Purchase #4	$13.39	5.486%	$14.1246	$14.12	$14.10	$14.10
Purchase #5	$41.30	9.449%	$45.2024	$45.20	$45.20	$45.20
Purchase #6	$211.67	13.333%	$239.892	$239.89	$239.90	$239.90
Purchase #7	$90.91	4.476%	$94.9791	$94.98	$95.00	$95.00
7 purchase totals =	$662.06		$721.8180	$721.81	$721.80	$721.80