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	$169.43	5.417%	$178.608	$178.61	$178.60	$178.60
Purchase #2	$165.74	4.105%	$172.5436	$172.54	$172.55	$172.50
Purchase #3	$189.36	12.704%	$213.4163	$213.42	$213.40	$213.40
Purchase #4	$35.25	5.442%	$37.1683	$37.17	$37.15	$37.20
Purchase #5	$46.39	13.750%	$52.7686	$52.77	$52.75	$52.80
Purchase #6	$144.50	5.242%	$152.0747	$152.07	$152.05	$152.10
Purchase #7	$48.50	4.782%	$50.8193	$50.82	$50.80	$50.80
7 purchase totals =	$799.17		$857.3988	$857.40	$857.30	$857.40