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	$27.71	4.205%	$28.8752	$28.88	$28.90	$28.90
Purchase #2	$129.52	11.635%	$144.5897	$144.59	$144.60	$144.60
Purchase #3	$127.66	11.120%	$141.8558	$141.86	$141.85	$141.90
Purchase #4	$73.57	13.823%	$83.7396	$83.74	$83.75	$83.70
Purchase #5	$109.53	8.778%	$119.1445	$119.14	$119.15	$119.10
Purchase #6	$15.59	13.670%	$17.7212	$17.72	$17.70	$17.70
Purchase #7	$245.88	3.785%	$255.1866	$255.19	$255.20	$255.20
7 purchase totals =	$729.46		$791.1126	$791.12	$791.15	$791.10