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	$82.79	9.779%	$90.886	$90.89	$90.90	$90.90
Purchase #2	$121.35	9.603%	$133.0032	$133.00	$133.00	$133.00
Purchase #3	$222.63	7.173%	$238.5992	$238.60	$238.60	$238.60
Purchase #4	$99.71	12.240%	$111.9145	$111.91	$111.90	$111.90
Purchase #5	$26.89	13.302%	$30.4669	$30.47	$30.45	$30.50
Purchase #6	$66.75	12.327%	$74.9783	$74.98	$75.00	$75.00
Purchase #7	$237.41	8.762%	$258.2119	$258.21	$258.20	$258.20
7 purchase totals =	$857.53		$938.0600	$938.06	$938.05	$938.10