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	$93.96	7.255%	$100.7768	$100.78	$100.80	$100.80
Purchase #2	$5.75	12.512%	$6.4694	$6.47	$6.45	$6.50
Purchase #3	$59.51	8.528%	$64.585	$64.59	$64.60	$64.60
Purchase #4	$29.87	9.814%	$32.8014	$32.80	$32.80	$32.80
Purchase #5	$151.94	5.333%	$160.043	$160.04	$160.05	$160.00
Purchase #6	$247.53	5.692%	$261.6194	$261.62	$261.60	$261.60
Purchase #7	$11.46	9.681%	$12.5694	$12.57	$12.55	$12.60
7 purchase totals =	$600.02		$638.8644	$638.87	$638.85	$638.90