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	$150.52	9.839%	$165.3297	$165.33	$165.35	$165.30
Purchase #2	$99.87	5.360%	$105.223	$105.22	$105.20	$105.20
Purchase #3	$7.50	3.314%	$7.7486	$7.75	$7.75	$7.70
Purchase #4	$18.27	3.700%	$18.946	$18.95	$18.95	$18.90
Purchase #5	$37.47	5.590%	$39.5646	$39.56	$39.55	$39.60
Purchase #6	$141.37	13.286%	$160.1524	$160.15	$160.15	$160.20
Purchase #7	$234.78	12.727%	$264.6605	$264.66	$264.65	$264.70
7 purchase totals =	$689.78		$761.6248	$761.62	$761.60	$761.60