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	$207.84	11.485%	$231.7104	$231.71	$231.70	$231.70
Purchase #2	$106.77	10.459%	$117.9371	$117.94	$117.95	$117.90
Purchase #3	$185.40	13.529%	$210.4828	$210.48	$210.50	$210.50
Purchase #4	$79.82	13.400%	$90.5159	$90.52	$90.50	$90.50
Purchase #5	$45.84	9.222%	$50.0674	$50.07	$50.05	$50.10
Purchase #6	$230.87	12.270%	$259.1977	$259.20	$259.20	$259.20
Purchase #7	$14.76	4.800%	$15.4685	$15.47	$15.45	$15.50
7 purchase totals =	$871.30		$975.3798	$975.39	$975.35	$975.40