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	$75.79	3.598%	$78.5169	$78.52	$78.50	$78.50
Purchase #2	$83.65	10.718%	$92.6156	$92.62	$92.60	$92.60
Purchase #3	$112.60	13.279%	$127.5522	$127.55	$127.55	$127.60
Purchase #4	$59.79	12.166%	$67.0641	$67.06	$67.05	$67.10
Purchase #5	$15.60	11.691%	$17.4238	$17.42	$17.40	$17.40
Purchase #6	$61.71	9.638%	$67.6576	$67.66	$67.65	$67.70
Purchase #7	$234.77	12.349%	$263.7617	$263.76	$263.75	$263.80
7 purchase totals =	$643.91		$714.5919	$714.59	$714.50	$714.70