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	$74.75	5.223%	$78.6542	$78.65	$78.65	$78.70
Purchase #2	$19.89	6.739%	$21.2304	$21.23	$21.25	$21.20
Purchase #3	$248.53	10.632%	$274.9537	$274.95	$274.95	$275.00
Purchase #4	$154.95	13.423%	$175.7489	$175.75	$175.75	$175.70
Purchase #5	$80.62	10.716%	$89.2592	$89.26	$89.25	$89.30
Purchase #6	$92.28	7.146%	$98.8743	$98.87	$98.85	$98.90
Purchase #7	$20.99	3.372%	$21.6978	$21.70	$21.70	$21.70
7 purchase totals =	$692.01		$760.4185	$760.41	$760.40	$760.50