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	$138.48	4.111%	$144.1729	$144.17	$144.15	$144.20
Purchase #2	$144.50	4.620%	$151.1759	$151.18	$151.20	$151.20
Purchase #3	$67.67	5.682%	$71.515	$71.52	$71.50	$71.50
Purchase #4	$107.70	3.261%	$111.2121	$111.21	$111.20	$111.20
Purchase #5	$64.54	10.140%	$71.0844	$71.08	$71.10	$71.10
Purchase #6	$224.99	13.271%	$254.8484	$254.85	$254.85	$254.80
Purchase #7	$34.50	6.608%	$36.7798	$36.78	$36.80	$36.80
7 purchase totals =	$782.38		$840.7885	$840.79	$840.80	$840.80