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	$86.78	4.668%	$90.8309	$90.83	$90.85	$90.80
Purchase #2	$144.38	13.547%	$163.9392	$163.94	$163.95	$163.90
Purchase #3	$11.34	7.124%	$12.1479	$12.15	$12.15	$12.10
Purchase #4	$85.67	6.120%	$90.913	$90.91	$90.90	$90.90
Purchase #5	$227.68	9.244%	$248.7267	$248.73	$248.75	$248.70
Purchase #6	$196.77	3.768%	$204.1843	$204.18	$204.20	$204.20
Purchase #7	$162.55	3.409%	$168.0913	$168.09	$168.10	$168.10
7 purchase totals =	$915.17		$978.8333	$978.83	$978.90	$978.70