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	$36.72	10.451%	$40.5576	$40.56	$40.55	$40.60
Purchase #2	$89.25	8.594%	$96.9201	$96.92	$96.90	$96.90
Purchase #3	$232.85	13.812%	$265.0112	$265.01	$265.00	$265.00
Purchase #4	$66.25	6.659%	$70.6616	$70.66	$70.65	$70.70
Purchase #5	$18.54	9.769%	$20.3512	$20.35	$20.35	$20.40
Purchase #6	$43.44	4.842%	$45.5434	$45.54	$45.55	$45.50
Purchase #7	$110.69	10.690%	$122.5228	$122.52	$122.50	$122.50
7 purchase totals =	$597.74		$661.5679	$661.56	$661.50	$661.60