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	$81.35	11.740%	$90.9005	$90.90	$90.90	$90.90
Purchase #2	$59.60	10.657%	$65.9516	$65.95	$65.95	$66.00
Purchase #3	$180.41	5.260%	$189.8996	$189.90	$189.90	$189.90
Purchase #4	$75.81	4.714%	$79.3837	$79.38	$79.40	$79.40
Purchase #5	$158.79	12.361%	$178.418	$178.42	$178.40	$178.40
Purchase #6	$116.40	11.233%	$129.4752	$129.48	$129.50	$129.50
Purchase #7	$122.96	7.256%	$131.882	$131.88	$131.90	$131.90
7 purchase totals =	$795.32		$865.9106	$865.91	$865.95	$866.00