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	$227.90	3.431%	$235.7192	$235.72	$235.70	$235.70
Purchase #2	$31.48	11.399%	$35.0684	$35.07	$35.05	$35.10
Purchase #3	$186.86	9.290%	$204.2193	$204.22	$204.20	$204.20
Purchase #4	$102.42	13.719%	$116.471	$116.47	$116.45	$116.50
Purchase #5	$117.69	8.158%	$127.2912	$127.29	$127.30	$127.30
Purchase #6	$48.37	7.828%	$52.1564	$52.16	$52.15	$52.20
Purchase #7	$74.74	8.218%	$80.8821	$80.88	$80.90	$80.90
7 purchase totals =	$789.46		$851.8076	$851.81	$851.75	$851.90