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	$89.51	3.185%	$92.3609	$92.36	$92.35	$92.40
Purchase #2	$23.76	5.713%	$25.1174	$25.12	$25.10	$25.10
Purchase #3	$132.94	7.411%	$142.7922	$142.79	$142.80	$142.80
Purchase #4	$33.28	12.510%	$37.4433	$37.44	$37.45	$37.40
Purchase #5	$75.28	3.672%	$78.0443	$78.04	$78.05	$78.00
Purchase #6	$73.28	6.191%	$77.8168	$77.82	$77.80	$77.80
Purchase #7	$187.45	13.319%	$212.4165	$212.42	$212.40	$212.40
7 purchase totals =	$615.50		$665.9914	$665.99	$665.95	$665.90