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	$150.39	9.821%	$165.1598	$165.16	$165.15	$165.20
Purchase #2	$145.42	11.749%	$162.5054	$162.51	$162.50	$162.50
Purchase #3	$176.76	6.603%	$188.4315	$188.43	$188.45	$188.40
Purchase #4	$150.62	12.800%	$169.8994	$169.90	$169.90	$169.90
Purchase #5	$97.45	12.599%	$109.7277	$109.73	$109.75	$109.70
Purchase #6	$33.27	6.812%	$35.5364	$35.54	$35.55	$35.50
Purchase #7	$70.46	10.240%	$77.6751	$77.68	$77.70	$77.70
7 purchase totals =	$824.37		$908.9353	$908.95	$909.00	$908.90