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	$35.84	7.321%	$38.4638	$38.46	$38.45	$38.50
Purchase #2	$160.27	12.416%	$180.1691	$180.17	$180.15	$180.20
Purchase #3	$35.78	13.391%	$40.5713	$40.57	$40.55	$40.60
Purchase #4	$157.55	5.690%	$166.5146	$166.51	$166.50	$166.50
Purchase #5	$30.44	10.538%	$33.6478	$33.65	$33.65	$33.60
Purchase #6	$238.57	7.328%	$256.0524	$256.05	$256.05	$256.10
Purchase #7	$161.60	4.668%	$169.1435	$169.14	$169.15	$169.10
7 purchase totals =	$820.05		$884.5625	$884.55	$884.50	$884.60