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	$48.27	7.193%	$51.7421	$51.74	$51.75	$51.70
Purchase #2	$248.40	4.111%	$258.6117	$258.61	$258.60	$258.60
Purchase #3	$20.40	7.568%	$21.9439	$21.94	$21.95	$21.90
Purchase #4	$71.45	5.192%	$75.1597	$75.16	$75.15	$75.20
Purchase #5	$62.91	3.542%	$65.1383	$65.14	$65.15	$65.10
Purchase #6	$42.44	7.735%	$45.7227	$45.72	$45.70	$45.70
Purchase #7	$104.57	6.870%	$111.754	$111.75	$111.75	$111.80
7 purchase totals =	$598.44		$630.0724	$630.06	$630.05	$630.00