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	$191.51	12.741%	$215.9103	$215.91	$215.90	$215.90
Purchase #2	$238.50	12.696%	$268.78	$268.78	$268.80	$268.80
Purchase #3	$9.83	13.388%	$11.146	$11.15	$11.15	$11.10
Purchase #4	$200.26	4.297%	$208.8652	$208.87	$208.85	$208.90
Purchase #5	$43.95	10.736%	$48.6685	$48.67	$48.65	$48.70
Purchase #6	$233.36	10.232%	$257.2374	$257.24	$257.25	$257.20
Purchase #7	$82.59	9.366%	$90.3254	$90.33	$90.35	$90.30
7 purchase totals =	$1,000.00		$1,100.9328	$1,100.95	$1,100.95	$1,100.90