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	$230.49	4.683%	$241.2838	$241.28	$241.30	$241.30
Purchase #2	$100.84	10.780%	$111.7106	$111.71	$111.70	$111.70
Purchase #3	$206.48	4.517%	$215.8067	$215.81	$215.80	$215.80
Purchase #4	$18.70	11.157%	$20.7864	$20.79	$20.80	$20.80
Purchase #5	$116.31	11.323%	$129.4798	$129.48	$129.50	$129.50
Purchase #6	$77.94	9.851%	$85.6179	$85.62	$85.60	$85.60
Purchase #7	$84.71	9.498%	$92.7558	$92.76	$92.75	$92.80
7 purchase totals =	$835.47		$897.4410	$897.45	$897.45	$897.50