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	$159.84	13.550%	$181.4983	$181.50	$181.50	$181.50
Purchase #2	$56.37	4.702%	$59.0205	$59.02	$59.00	$59.00
Purchase #3	$98.94	8.423%	$107.2737	$107.27	$107.25	$107.30
Purchase #4	$172.63	6.149%	$183.245	$183.25	$183.25	$183.20
Purchase #5	$22.31	10.833%	$24.7268	$24.73	$24.75	$24.70
Purchase #6	$170.91	8.720%	$185.8134	$185.81	$185.80	$185.80
Purchase #7	$123.69	4.176%	$128.8553	$128.86	$128.85	$128.90
7 purchase totals =	$804.69		$870.4330	$870.44	$870.40	$870.40