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	$65.77	5.543%	$69.4156	$69.42	$69.40	$69.40
Purchase #2	$43.92	3.719%	$45.5534	$45.55	$45.55	$45.60
Purchase #3	$165.69	8.456%	$179.7007	$179.70	$179.70	$179.70
Purchase #4	$234.73	8.423%	$254.5013	$254.50	$254.50	$254.50
Purchase #5	$111.42	10.651%	$123.2873	$123.29	$123.30	$123.30
Purchase #6	$138.97	12.170%	$155.8826	$155.88	$155.90	$155.90
Purchase #7	$114.77	7.182%	$123.0128	$123.01	$123.00	$123.00
7 purchase totals =	$875.27		$951.3537	$951.35	$951.35	$951.40