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	$80.41	10.821%	$89.1112	$89.11	$89.10	$89.10
Purchase #2	$66.45	12.541%	$74.7835	$74.78	$74.80	$74.80
Purchase #3	$86.25	7.698%	$92.8895	$92.89	$92.90	$92.90
Purchase #4	$130.56	10.715%	$144.5495	$144.55	$144.55	$144.50
Purchase #5	$231.93	13.529%	$263.3078	$263.31	$263.30	$263.30
Purchase #6	$171.70	8.161%	$185.7124	$185.71	$185.70	$185.70
Purchase #7	$21.52	5.806%	$22.7695	$22.77	$22.75	$22.80
7 purchase totals =	$788.82		$873.1234	$873.12	$873.10	$873.10