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	$89.60	11.485%	$99.8906	$99.89	$99.90	$99.90
Purchase #2	$53.67	7.485%	$57.6872	$57.69	$57.70	$57.70
Purchase #3	$207.67	9.540%	$227.4817	$227.48	$227.50	$227.50
Purchase #4	$17.47	9.582%	$19.144	$19.14	$19.15	$19.10
Purchase #5	$63.56	5.253%	$66.8988	$66.90	$66.90	$66.90
Purchase #6	$139.30	4.654%	$145.783	$145.78	$145.80	$145.80
Purchase #7	$51.35	8.202%	$55.5617	$55.56	$55.55	$55.60
7 purchase totals =	$622.62		$672.4470	$672.44	$672.50	$672.50