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	$101.60	8.187%	$109.918	$109.92	$109.90	$109.90
Purchase #2	$48.49	11.507%	$54.0697	$54.07	$54.05	$54.10
Purchase #3	$133.76	8.229%	$144.7671	$144.77	$144.75	$144.80
Purchase #4	$89.30	11.335%	$99.4222	$99.42	$99.40	$99.40
Purchase #5	$89.57	13.844%	$101.9701	$101.97	$101.95	$102.00
Purchase #6	$102.47	6.739%	$109.3755	$109.38	$109.40	$109.40
Purchase #7	$201.28	9.608%	$220.619	$220.62	$220.60	$220.60
7 purchase totals =	$766.47		$840.1416	$840.15	$840.05	$840.20