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	$111.77	11.417%	$124.5308	$124.53	$124.55	$124.50
Purchase #2	$197.90	11.871%	$221.3927	$221.39	$221.40	$221.40
Purchase #3	$123.52	8.345%	$133.8277	$133.83	$133.85	$133.80
Purchase #4	$123.86	13.217%	$140.2306	$140.23	$140.25	$140.20
Purchase #5	$235.77	10.596%	$260.7522	$260.75	$260.75	$260.80
Purchase #6	$233.92	9.337%	$255.7611	$255.76	$255.75	$255.80
Purchase #7	$141.33	8.848%	$153.8349	$153.83	$153.85	$153.80
7 purchase totals =	$1,168.07		$1,290.3300	$1,290.32	$1,290.40	$1,290.30