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	$18.69	9.793%	$20.5203	$20.52	$20.50	$20.50
Purchase #2	$27.64	5.556%	$29.1757	$29.18	$29.20	$29.20
Purchase #3	$138.91	8.196%	$150.2951	$150.30	$150.30	$150.30
Purchase #4	$147.76	9.702%	$162.0957	$162.10	$162.10	$162.10
Purchase #5	$13.62	13.570%	$15.4682	$15.47	$15.45	$15.50
Purchase #6	$157.60	9.290%	$172.241	$172.24	$172.25	$172.20
Purchase #7	$211.61	7.330%	$227.121	$227.12	$227.10	$227.10
7 purchase totals =	$715.83		$776.9170	$776.93	$776.90	$776.90