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	$100.59	8.248%	$108.8867	$108.89	$108.90	$108.90
Purchase #2	$147.39	5.847%	$156.0079	$156.01	$156.00	$156.00
Purchase #3	$143.87	5.479%	$151.7526	$151.75	$151.75	$151.80
Purchase #4	$247.36	3.325%	$255.5847	$255.58	$255.60	$255.60
Purchase #5	$6.44	7.529%	$6.9249	$6.92	$6.90	$6.90
Purchase #6	$92.35	10.445%	$101.996	$102.00	$102.00	$102.00
Purchase #7	$91.59	13.119%	$103.6057	$103.61	$103.60	$103.60
7 purchase totals =	$829.59		$884.7585	$884.76	$884.75	$884.80