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	$13.55	13.587%	$15.391	$15.39	$15.40	$15.40
Purchase #2	$217.45	5.648%	$229.7316	$229.73	$229.75	$229.70
Purchase #3	$59.93	11.713%	$66.9496	$66.95	$66.95	$66.90
Purchase #4	$164.33	11.460%	$183.1622	$183.16	$183.15	$183.20
Purchase #5	$205.90	8.515%	$223.4324	$223.43	$223.45	$223.40
Purchase #6	$158.96	8.368%	$172.2618	$172.26	$172.25	$172.30
Purchase #7	$117.90	13.839%	$134.2162	$134.22	$134.20	$134.20
7 purchase totals =	$938.02		$1,025.1448	$1,025.14	$1,025.15	$1,025.10