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	$134.48	11.610%	$150.0931	$150.09	$150.10	$150.10
Purchase #2	$215.75	13.332%	$244.5138	$244.51	$244.50	$244.50
Purchase #3	$124.93	12.502%	$140.5487	$140.55	$140.55	$140.50
Purchase #4	$109.54	6.277%	$116.4158	$116.42	$116.40	$116.40
Purchase #5	$83.55	3.766%	$86.6965	$86.70	$86.70	$86.70
Purchase #6	$99.92	11.295%	$111.206	$111.21	$111.20	$111.20
Purchase #7	$120.45	5.265%	$126.7917	$126.79	$126.80	$126.80
7 purchase totals =	$888.62		$976.2656	$976.27	$976.25	$976.20