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	$212.51	6.279%	$225.8535	$225.85	$225.85	$225.90
Purchase #2	$181.59	5.160%	$190.96	$190.96	$190.95	$191.00
Purchase #3	$49.61	11.839%	$55.4833	$55.48	$55.50	$55.50
Purchase #4	$132.80	12.649%	$149.5979	$149.60	$149.60	$149.60
Purchase #5	$118.39	11.287%	$131.7527	$131.75	$131.75	$131.80
Purchase #6	$158.26	4.526%	$165.4228	$165.42	$165.40	$165.40
Purchase #7	$47.67	4.218%	$49.6807	$49.68	$49.70	$49.70
7 purchase totals =	$900.83		$968.7509	$968.74	$968.75	$968.90