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	$101.50	6.598%	$108.197	$108.20	$108.20	$108.20
Purchase #2	$80.89	11.392%	$90.105	$90.11	$90.10	$90.10
Purchase #3	$110.37	12.235%	$123.8738	$123.87	$123.85	$123.90
Purchase #4	$139.36	4.479%	$145.6019	$145.60	$145.60	$145.60
Purchase #5	$158.29	10.774%	$175.3442	$175.34	$175.35	$175.30
Purchase #6	$122.38	8.347%	$132.5951	$132.60	$132.60	$132.60
Purchase #7	$122.43	8.355%	$132.659	$132.66	$132.65	$132.70
7 purchase totals =	$835.22		$908.3760	$908.38	$908.35	$908.40