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	$168.88	9.865%	$185.54	$185.54	$185.55	$185.50
Purchase #2	$247.60	12.485%	$278.5129	$278.51	$278.50	$278.50
Purchase #3	$102.53	9.392%	$112.1596	$112.16	$112.15	$112.20
Purchase #4	$47.90	5.442%	$50.5067	$50.51	$50.50	$50.50
Purchase #5	$24.70	11.812%	$27.6176	$27.62	$27.60	$27.60
Purchase #6	$65.71	6.312%	$69.8576	$69.86	$69.85	$69.90
Purchase #7	$15.43	11.576%	$17.2162	$17.22	$17.20	$17.20
7 purchase totals =	$672.75		$741.4106	$741.42	$741.35	$741.40