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	$146.47	13.339%	$166.0076	$166.01	$166.00	$166.00
Purchase #2	$129.61	13.738%	$147.4158	$147.42	$147.40	$147.40
Purchase #3	$214.49	6.227%	$227.8463	$227.85	$227.85	$227.80
Purchase #4	$225.64	6.714%	$240.7895	$240.79	$240.80	$240.80
Purchase #5	$99.47	4.398%	$103.8447	$103.84	$103.85	$103.80
Purchase #6	$102.96	6.649%	$109.8058	$109.81	$109.80	$109.80
Purchase #7	$22.48	4.203%	$23.4248	$23.42	$23.40	$23.40
7 purchase totals =	$941.12		$1,019.1345	$1,019.14	$1,019.10	$1,019.00