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	$104.28	3.873%	$108.3188	$108.32	$108.30	$108.30
Purchase #2	$54.61	13.290%	$61.8677	$61.87	$61.85	$61.90
Purchase #3	$169.84	8.595%	$184.4377	$184.44	$184.45	$184.40
Purchase #4	$91.69	11.136%	$101.9006	$101.90	$101.90	$101.90
Purchase #5	$81.65	10.860%	$90.5172	$90.52	$90.50	$90.50
Purchase #6	$173.75	11.325%	$193.4272	$193.43	$193.45	$193.40
Purchase #7	$250.51	6.368%	$266.4625	$266.46	$266.45	$266.50
7 purchase totals =	$926.33		$1,006.9317	$1,006.94	$1,006.90	$1,006.90