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	$41.28	5.139%	$43.4014	$43.40	$43.40	$43.40
Purchase #2	$50.31	13.764%	$57.2347	$57.23	$57.25	$57.20
Purchase #3	$30.83	3.365%	$31.8674	$31.87	$31.85	$31.90
Purchase #4	$197.55	9.119%	$215.5646	$215.56	$215.55	$215.60
Purchase #5	$25.72	13.112%	$29.0924	$29.09	$29.10	$29.10
Purchase #6	$100.48	11.127%	$111.6604	$111.66	$111.65	$111.70
Purchase #7	$230.45	12.337%	$258.8806	$258.88	$258.90	$258.90
7 purchase totals =	$676.62		$747.7015	$747.69	$747.70	$747.80