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	$49.69	7.607%	$53.4699	$53.47	$53.45	$53.50
Purchase #2	$56.32	6.111%	$59.7617	$59.76	$59.75	$59.80
Purchase #3	$237.53	6.138%	$252.1096	$252.11	$252.10	$252.10
Purchase #4	$165.82	8.799%	$180.4105	$180.41	$180.40	$180.40
Purchase #5	$56.58	5.762%	$59.8401	$59.84	$59.85	$59.80
Purchase #6	$19.87	4.280%	$20.7204	$20.72	$20.70	$20.70
Purchase #7	$19.48	8.259%	$21.0889	$21.09	$21.10	$21.10
7 purchase totals =	$605.29		$647.4011	$647.40	$647.35	$647.40