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	$73.99	5.466%	$78.0343	$78.03	$78.05	$78.00
Purchase #2	$104.87	9.531%	$114.8652	$114.87	$114.85	$114.90
Purchase #3	$21.95	11.692%	$24.5164	$24.52	$24.50	$24.50
Purchase #4	$127.63	10.854%	$141.483	$141.48	$141.50	$141.50
Purchase #5	$67.77	13.195%	$76.7123	$76.71	$76.70	$76.70
Purchase #6	$70.78	12.513%	$79.6367	$79.64	$79.65	$79.60
Purchase #7	$169.73	10.698%	$187.8877	$187.89	$187.90	$187.90
7 purchase totals =	$636.72		$703.1356	$703.14	$703.15	$703.10