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	$110.43	11.461%	$123.0864	$123.09	$123.10	$123.10
Purchase #2	$60.38	9.468%	$66.0968	$66.10	$66.10	$66.10
Purchase #3	$244.26	8.435%	$264.8633	$264.86	$264.85	$264.90
Purchase #4	$83.33	7.178%	$89.3114	$89.31	$89.30	$89.30
Purchase #5	$119.37	12.808%	$134.6589	$134.66	$134.65	$134.70
Purchase #6	$53.41	4.809%	$55.9785	$55.98	$56.00	$56.00
Purchase #7	$143.87	10.269%	$158.644	$158.64	$158.65	$158.60
7 purchase totals =	$815.05		$892.6393	$892.64	$892.65	$892.70