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	$40.68	3.742%	$42.2022	$42.20	$42.20	$42.20
Purchase #2	$83.27	11.109%	$92.5205	$92.52	$92.50	$92.50
Purchase #3	$79.59	12.702%	$89.6995	$89.70	$89.70	$89.70
Purchase #4	$170.34	9.245%	$186.0879	$186.09	$186.10	$186.10
Purchase #5	$216.56	13.818%	$246.4843	$246.48	$246.50	$246.50
Purchase #6	$172.53	10.806%	$191.1736	$191.17	$191.15	$191.20
Purchase #7	$34.61	8.418%	$37.5235	$37.52	$37.50	$37.50
7 purchase totals =	$797.58		$885.6915	$885.68	$885.65	$885.70