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	$140.83	11.500%	$157.0255	$157.03	$157.05	$157.00
Purchase #2	$86.54	6.164%	$91.8743	$91.87	$91.85	$91.90
Purchase #3	$165.85	8.838%	$180.5078	$180.51	$180.50	$180.50
Purchase #4	$102.64	13.458%	$116.4533	$116.45	$116.45	$116.50
Purchase #5	$80.74	11.111%	$89.711	$89.71	$89.70	$89.70
Purchase #6	$199.56	10.819%	$221.1504	$221.15	$221.15	$221.20
Purchase #7	$116.65	9.544%	$127.7831	$127.78	$127.80	$127.80
7 purchase totals =	$892.81		$984.5054	$984.50	$984.50	$984.60