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	$156.98	13.606%	$178.3387	$178.34	$178.35	$178.30
Purchase #2	$54.96	6.847%	$58.7231	$58.72	$58.70	$58.70
Purchase #3	$56.33	5.810%	$59.6028	$59.60	$59.60	$59.60
Purchase #4	$75.73	8.482%	$82.1534	$82.15	$82.15	$82.20
Purchase #5	$137.87	5.475%	$145.4184	$145.42	$145.40	$145.40
Purchase #6	$142.44	11.563%	$158.9103	$158.91	$158.90	$158.90
Purchase #7	$169.43	12.398%	$190.4359	$190.44	$190.45	$190.40
7 purchase totals =	$793.74		$873.5826	$873.58	$873.55	$873.50