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	$109.49	12.578%	$123.2617	$123.26	$123.25	$123.30
Purchase #2	$23.28	9.225%	$25.4276	$25.43	$25.45	$25.40
Purchase #3	$32.79	11.800%	$36.6592	$36.66	$36.65	$36.70
Purchase #4	$189.85	3.374%	$196.2555	$196.26	$196.25	$196.30
Purchase #5	$122.32	6.195%	$129.8977	$129.90	$129.90	$129.90
Purchase #6	$58.95	13.366%	$66.8293	$66.83	$66.85	$66.80
Purchase #7	$127.34	13.531%	$144.5704	$144.57	$144.55	$144.60
7 purchase totals =	$664.02		$722.9014	$722.91	$722.90	$723.00