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	$37.97	12.211%	$42.6065	$42.61	$42.60	$42.60
Purchase #2	$41.62	4.374%	$43.4405	$43.44	$43.45	$43.40
Purchase #3	$94.33	11.246%	$104.9384	$104.94	$104.95	$104.90
Purchase #4	$62.93	7.634%	$67.7341	$67.73	$67.75	$67.70
Purchase #5	$141.57	11.213%	$157.4442	$157.44	$157.45	$157.40
Purchase #6	$18.57	7.447%	$19.9529	$19.95	$19.95	$20.00
Purchase #7	$234.52	9.184%	$256.0583	$256.06	$256.05	$256.10
7 purchase totals =	$631.51		$692.1749	$692.17	$692.20	$692.10