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	$127.70	13.560%	$145.0161	$145.02	$145.00	$145.00
Purchase #2	$80.45	12.845%	$90.7838	$90.78	$90.80	$90.80
Purchase #3	$130.49	4.294%	$136.0932	$136.09	$136.10	$136.10
Purchase #4	$131.26	3.819%	$136.2728	$136.27	$136.25	$136.30
Purchase #5	$113.40	12.322%	$127.3731	$127.37	$127.35	$127.40
Purchase #6	$130.85	6.463%	$139.3068	$139.31	$139.30	$139.30
Purchase #7	$174.62	4.396%	$182.2963	$182.30	$182.30	$182.30
7 purchase totals =	$888.77		$957.1421	$957.14	$957.10	$957.20