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	$7.30	7.149%	$7.8219	$7.82	$7.80	$7.80
Purchase #2	$80.51	12.184%	$90.3193	$90.32	$90.30	$90.30
Purchase #3	$159.76	13.262%	$180.9474	$180.95	$180.95	$180.90
Purchase #4	$158.97	5.649%	$167.9502	$167.95	$167.95	$168.00
Purchase #5	$226.26	6.133%	$240.1365	$240.14	$240.15	$240.10
Purchase #6	$88.77	11.204%	$98.7158	$98.72	$98.70	$98.70
Purchase #7	$198.70	13.674%	$225.8702	$225.87	$225.85	$225.90
7 purchase totals =	$920.27		$1,011.7613	$1,011.77	$1,011.70	$1,011.70