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	$9.87	5.355%	$10.3985	$10.40	$10.40	$10.40
Purchase #2	$156.98	7.455%	$168.6829	$168.68	$168.70	$168.70
Purchase #3	$163.30	5.740%	$172.6734	$172.67	$172.65	$172.70
Purchase #4	$210.64	3.854%	$218.7581	$218.76	$218.75	$218.80
Purchase #5	$151.54	13.853%	$172.5328	$172.53	$172.55	$172.50
Purchase #6	$73.82	6.479%	$78.6028	$78.60	$78.60	$78.60
Purchase #7	$6.80	7.624%	$7.3184	$7.32	$7.30	$7.30
7 purchase totals =	$772.95		$828.9669	$828.96	$828.95	$829.00