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	$31.30	8.490%	$33.9574	$33.96	$33.95	$34.00
Purchase #2	$55.73	6.333%	$59.2594	$59.26	$59.25	$59.30
Purchase #3	$102.28	13.814%	$116.409	$116.41	$116.40	$116.40
Purchase #4	$26.66	10.780%	$29.5339	$29.53	$29.55	$29.50
Purchase #5	$225.96	9.504%	$247.4352	$247.44	$247.45	$247.40
Purchase #6	$224.80	13.719%	$255.6403	$255.64	$255.65	$255.60
Purchase #7	$113.33	9.319%	$123.8912	$123.89	$123.90	$123.90
7 purchase totals =	$780.06		$866.1264	$866.13	$866.15	$866.10