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	$51.92	12.617%	$58.4707	$58.47	$58.45	$58.50
Purchase #2	$71.32	12.493%	$80.23	$80.23	$80.25	$80.20
Purchase #3	$194.35	13.108%	$219.8254	$219.83	$219.85	$219.80
Purchase #4	$167.69	9.109%	$182.9649	$182.96	$182.95	$183.00
Purchase #5	$18.96	13.477%	$21.5152	$21.52	$21.50	$21.50
Purchase #6	$138.31	9.719%	$151.7523	$151.75	$151.75	$151.80
Purchase #7	$79.76	11.715%	$89.1039	$89.10	$89.10	$89.10
7 purchase totals =	$722.31		$803.8624	$803.86	$803.85	$803.90