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	$57.76	3.151%	$59.58	$59.58	$59.60	$59.60
Purchase #2	$229.53	7.548%	$246.8549	$246.85	$246.85	$246.90
Purchase #3	$88.51	11.820%	$98.9719	$98.97	$98.95	$99.00
Purchase #4	$54.69	13.647%	$62.1535	$62.15	$62.15	$62.20
Purchase #5	$60.83	10.352%	$67.1271	$67.13	$67.15	$67.10
Purchase #6	$248.54	10.446%	$274.5025	$274.50	$274.50	$274.50
Purchase #7	$248.25	3.153%	$256.0773	$256.08	$256.10	$256.10
7 purchase totals =	$988.11		$1,065.2672	$1,065.26	$1,065.30	$1,065.40