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	$115.77	8.103%	$125.1508	$125.15	$125.15	$125.20
Purchase #2	$84.77	6.494%	$90.275	$90.28	$90.30	$90.30
Purchase #3	$12.40	7.711%	$13.3562	$13.36	$13.35	$13.40
Purchase #4	$134.56	13.403%	$152.5951	$152.60	$152.60	$152.60
Purchase #5	$18.54	10.698%	$20.5234	$20.52	$20.50	$20.50
Purchase #6	$62.35	6.452%	$66.3728	$66.37	$66.35	$66.40
Purchase #7	$28.87	10.255%	$31.8306	$31.83	$31.85	$31.80
7 purchase totals =	$457.26		$500.1039	$500.11	$500.10	$500.20