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	$56.26	9.821%	$61.7853	$61.79	$61.80	$61.80
Purchase #2	$135.59	4.470%	$141.6509	$141.65	$141.65	$141.70
Purchase #3	$197.47	11.445%	$220.0704	$220.07	$220.05	$220.10
Purchase #4	$174.59	12.738%	$196.8293	$196.83	$196.85	$196.80
Purchase #5	$236.41	8.868%	$257.3748	$257.37	$257.35	$257.40
Purchase #6	$33.75	5.233%	$35.5161	$35.52	$35.50	$35.50
Purchase #7	$50.50	11.751%	$56.4343	$56.43	$56.45	$56.40
7 purchase totals =	$884.57		$969.6611	$969.66	$969.65	$969.70