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	$192.51	8.667%	$209.1948	$209.19	$209.20	$209.20
Purchase #2	$39.64	7.176%	$42.4846	$42.48	$42.50	$42.50
Purchase #3	$7.65	3.451%	$7.914	$7.91	$7.90	$7.90
Purchase #4	$93.99	6.570%	$100.1651	$100.17	$100.15	$100.20
Purchase #5	$230.85	3.672%	$239.3268	$239.33	$239.35	$239.30
Purchase #6	$58.73	12.667%	$66.1693	$66.17	$66.15	$66.20
Purchase #7	$94.65	11.395%	$105.4354	$105.44	$105.45	$105.40
7 purchase totals =	$718.02		$770.6900	$770.69	$770.70	$770.70