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	$38.92	7.760%	$41.9402	$41.94	$41.95	$41.90
Purchase #2	$20.99	4.295%	$21.8915	$21.89	$21.90	$21.90
Purchase #3	$116.96	13.297%	$132.5122	$132.51	$132.50	$132.50
Purchase #4	$250.26	3.265%	$258.431	$258.43	$258.45	$258.40
Purchase #5	$98.96	11.300%	$110.1425	$110.14	$110.15	$110.10
Purchase #6	$40.44	12.737%	$45.5908	$45.59	$45.60	$45.60
Purchase #7	$159.25	8.636%	$173.0028	$173.00	$173.00	$173.00
7 purchase totals =	$725.78		$783.5110	$783.50	$783.55	$783.40