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	$84.37	7.166%	$90.416	$90.42	$90.40	$90.40
Purchase #2	$74.28	4.244%	$77.4324	$77.43	$77.45	$77.40
Purchase #3	$139.34	9.308%	$152.3098	$152.31	$152.30	$152.30
Purchase #4	$35.66	12.361%	$40.0679	$40.07	$40.05	$40.10
Purchase #5	$242.47	3.558%	$251.0971	$251.10	$251.10	$251.10
Purchase #6	$73.90	5.625%	$78.0569	$78.06	$78.05	$78.10
Purchase #7	$169.61	11.496%	$189.1084	$189.11	$189.10	$189.10
7 purchase totals =	$819.63		$878.4885	$878.50	$878.45	$878.50