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	$123.83	13.506%	$140.5545	$140.55	$140.55	$140.60
Purchase #2	$169.77	11.404%	$189.1306	$189.13	$189.15	$189.10
Purchase #3	$156.36	12.547%	$175.9785	$175.98	$176.00	$176.00
Purchase #4	$59.89	9.647%	$65.6676	$65.67	$65.65	$65.70
Purchase #5	$103.84	4.565%	$108.5803	$108.58	$108.60	$108.60
Purchase #6	$76.56	4.491%	$79.9983	$80.00	$80.00	$80.00
Purchase #7	$74.72	10.362%	$82.4625	$82.46	$82.45	$82.50
7 purchase totals =	$764.97		$842.3723	$842.37	$842.40	$842.50