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	$134.54	4.305%	$140.3319	$140.33	$140.35	$140.30
Purchase #2	$156.69	7.494%	$168.4323	$168.43	$168.45	$168.40
Purchase #3	$41.71	6.667%	$44.4908	$44.49	$44.50	$44.50
Purchase #4	$219.36	3.690%	$227.4544	$227.45	$227.45	$227.50
Purchase #5	$80.66	12.770%	$90.9603	$90.96	$90.95	$91.00
Purchase #6	$7.32	13.838%	$8.3329	$8.33	$8.35	$8.30
Purchase #7	$56.60	10.111%	$62.3228	$62.32	$62.30	$62.30
7 purchase totals =	$696.88		$742.3254	$742.31	$742.35	$742.30