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	$17.29	13.185%	$19.5697	$19.57	$19.55	$19.60
Purchase #2	$120.73	5.353%	$127.1927	$127.19	$127.20	$127.20
Purchase #3	$133.35	13.461%	$151.3002	$151.30	$151.30	$151.30
Purchase #4	$229.62	10.781%	$254.3753	$254.38	$254.40	$254.40
Purchase #5	$250.79	9.686%	$275.0815	$275.08	$275.10	$275.10
Purchase #6	$102.94	10.481%	$113.7291	$113.73	$113.75	$113.70
Purchase #7	$36.59	10.818%	$40.5483	$40.55	$40.55	$40.50
7 purchase totals =	$891.31		$981.7968	$981.80	$981.85	$981.80