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	$171.93	6.422%	$182.9713	$182.97	$182.95	$183.00
Purchase #2	$174.58	6.846%	$186.5317	$186.53	$186.55	$186.50
Purchase #3	$20.39	4.373%	$21.2817	$21.28	$21.30	$21.30
Purchase #4	$67.46	4.138%	$70.2515	$70.25	$70.25	$70.30
Purchase #5	$139.37	3.847%	$144.7316	$144.73	$144.75	$144.70
Purchase #6	$100.42	11.348%	$111.8157	$111.82	$111.80	$111.80
Purchase #7	$229.41	11.186%	$255.0718	$255.07	$255.05	$255.10
7 purchase totals =	$903.56		$972.6553	$972.65	$972.65	$972.70