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	$92.69	6.710%	$98.9095	$98.91	$98.90	$98.90
Purchase #2	$30.36	4.608%	$31.759	$31.76	$31.75	$31.80
Purchase #3	$46.77	13.379%	$53.0274	$53.03	$53.05	$53.00
Purchase #4	$161.87	13.190%	$183.2207	$183.22	$183.20	$183.20
Purchase #5	$70.26	12.204%	$78.8345	$78.83	$78.85	$78.80
Purchase #6	$59.42	4.256%	$61.9489	$61.95	$61.95	$61.90
Purchase #7	$143.75	10.239%	$158.4686	$158.47	$158.45	$158.50
7 purchase totals =	$605.12		$666.1686	$666.17	$666.15	$666.10