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	$137.69	9.513%	$150.7884	$150.79	$150.80	$150.80
Purchase #2	$36.84	12.256%	$41.3551	$41.36	$41.35	$41.40
Purchase #3	$228.78	10.761%	$253.399	$253.40	$253.40	$253.40
Purchase #4	$96.99	3.493%	$100.3779	$100.38	$100.40	$100.40
Purchase #5	$24.92	3.159%	$25.7072	$25.71	$25.70	$25.70
Purchase #6	$100.81	10.265%	$111.1581	$111.16	$111.15	$111.20
Purchase #7	$100.66	6.673%	$107.377	$107.38	$107.40	$107.40
7 purchase totals =	$726.69		$790.1627	$790.18	$790.20	$790.30