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	$42.44	7.196%	$45.494	$45.49	$45.50	$45.50
Purchase #2	$179.29	8.510%	$194.5476	$194.55	$194.55	$194.50
Purchase #3	$51.85	13.771%	$58.9903	$58.99	$59.00	$59.00
Purchase #4	$31.29	3.337%	$32.3341	$32.33	$32.35	$32.30
Purchase #5	$184.78	3.839%	$191.8737	$191.87	$191.85	$191.90
Purchase #6	$159.72	13.684%	$181.5761	$181.58	$181.60	$181.60
Purchase #7	$20.74	3.680%	$21.5032	$21.50	$21.50	$21.50
7 purchase totals =	$670.11		$726.3190	$726.31	$726.35	$726.30