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	$61.47	9.787%	$67.4861	$67.49	$67.50	$67.50
Purchase #2	$193.39	7.707%	$208.2946	$208.29	$208.30	$208.30
Purchase #3	$35.49	7.171%	$38.035	$38.04	$38.05	$38.00
Purchase #4	$130.95	10.485%	$144.6801	$144.68	$144.70	$144.70
Purchase #5	$130.96	11.123%	$145.5267	$145.53	$145.55	$145.50
Purchase #6	$10.85	5.741%	$11.4729	$11.47	$11.45	$11.50
Purchase #7	$217.26	3.253%	$224.3275	$224.33	$224.35	$224.30
7 purchase totals =	$780.37		$839.8229	$839.83	$839.90	$839.80