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	$35.84	3.727%	$37.1758	$37.18	$37.20	$37.20
Purchase #2	$215.42	3.226%	$222.3694	$222.37	$222.35	$222.40
Purchase #3	$140.39	10.382%	$154.9653	$154.97	$154.95	$155.00
Purchase #4	$114.89	7.453%	$123.4528	$123.45	$123.45	$123.50
Purchase #5	$26.58	13.565%	$30.1856	$30.19	$30.20	$30.20
Purchase #6	$139.40	4.172%	$145.2158	$145.22	$145.20	$145.20
Purchase #7	$165.38	6.124%	$175.5079	$175.51	$175.50	$175.50
7 purchase totals =	$837.90		$888.8726	$888.89	$888.85	$889.00