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	$95.87	6.868%	$102.4544	$102.45	$102.45	$102.50
Purchase #2	$176.70	13.368%	$200.3213	$200.32	$200.30	$200.30
Purchase #3	$130.68	12.400%	$146.8843	$146.88	$146.90	$146.90
Purchase #4	$74.55	9.251%	$81.4466	$81.45	$81.45	$81.40
Purchase #5	$89.90	10.256%	$99.1201	$99.12	$99.10	$99.10
Purchase #6	$143.42	6.272%	$152.4153	$152.42	$152.40	$152.40
Purchase #7	$198.38	9.327%	$216.8829	$216.88	$216.90	$216.90
7 purchase totals =	$909.50		$999.5249	$999.52	$999.50	$999.50