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	$225.85	13.448%	$256.2223	$256.22	$256.20	$256.20
Purchase #2	$124.43	5.211%	$130.914	$130.91	$130.90	$130.90
Purchase #3	$170.73	11.737%	$190.7686	$190.77	$190.75	$190.80
Purchase #4	$70.39	12.542%	$79.2183	$79.22	$79.20	$79.20
Purchase #5	$95.87	4.698%	$100.374	$100.37	$100.35	$100.40
Purchase #6	$57.83	6.456%	$61.5635	$61.56	$61.55	$61.60
Purchase #7	$9.66	7.738%	$10.4075	$10.41	$10.40	$10.40
7 purchase totals =	$754.76		$829.4682	$829.46	$829.35	$829.50