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	$10.97	7.689%	$11.8135	$11.81	$11.80	$11.80
Purchase #2	$63.62	13.350%	$72.1133	$72.11	$72.10	$72.10
Purchase #3	$11.72	7.426%	$12.5903	$12.59	$12.60	$12.60
Purchase #4	$92.54	4.678%	$96.869	$96.87	$96.85	$96.90
Purchase #5	$65.78	7.716%	$70.8556	$70.86	$70.85	$70.90
Purchase #6	$116.28	12.520%	$130.8383	$130.84	$130.85	$130.80
Purchase #7	$199.85	10.350%	$220.5345	$220.53	$220.55	$220.50
7 purchase totals =	$560.76		$615.6145	$615.61	$615.60	$615.60