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	$87.51	3.818%	$90.8511	$90.85	$90.85	$90.90
Purchase #2	$186.77	5.396%	$196.8481	$196.85	$196.85	$196.80
Purchase #3	$162.93	10.779%	$180.4922	$180.49	$180.50	$180.50
Purchase #4	$56.69	6.600%	$60.4315	$60.43	$60.45	$60.40
Purchase #5	$115.48	7.795%	$124.4817	$124.48	$124.50	$124.50
Purchase #6	$222.52	12.375%	$250.0569	$250.06	$250.05	$250.10
Purchase #7	$73.84	8.435%	$80.0684	$80.07	$80.05	$80.10
7 purchase totals =	$905.74		$983.2299	$983.23	$983.25	$983.30