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	$62.44	3.316%	$64.5105	$64.51	$64.50	$64.50
Purchase #2	$80.70	3.623%	$83.6238	$83.62	$83.60	$83.60
Purchase #3	$250.40	11.589%	$279.4189	$279.42	$279.40	$279.40
Purchase #4	$71.25	10.613%	$78.8118	$78.81	$78.80	$78.80
Purchase #5	$10.41	12.173%	$11.6772	$11.68	$11.70	$11.70
Purchase #6	$248.33	11.756%	$277.5237	$277.52	$277.50	$277.50
Purchase #7	$63.61	12.770%	$71.733	$71.73	$71.75	$71.70
7 purchase totals =	$787.14		$867.2989	$867.29	$867.25	$867.20