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	$156.44	10.169%	$172.3484	$172.35	$172.35	$172.30
Purchase #2	$35.97	8.793%	$39.1328	$39.13	$39.15	$39.10
Purchase #3	$167.49	13.511%	$190.1196	$190.12	$190.10	$190.10
Purchase #4	$200.40	12.587%	$225.6243	$225.62	$225.60	$225.60
Purchase #5	$70.89	13.569%	$80.5091	$80.51	$80.50	$80.50
Purchase #6	$124.65	6.537%	$132.7984	$132.80	$132.80	$132.80
Purchase #7	$82.58	10.618%	$91.3483	$91.35	$91.35	$91.30
7 purchase totals =	$838.42		$931.8809	$931.88	$931.85	$931.70