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	$77.72	6.652%	$82.8899	$82.89	$82.90	$82.90
Purchase #2	$203.58	13.403%	$230.8658	$230.87	$230.85	$230.90
Purchase #3	$6.42	10.340%	$7.0838	$7.08	$7.10	$7.10
Purchase #4	$16.50	5.727%	$17.445	$17.45	$17.45	$17.40
Purchase #5	$86.69	7.159%	$92.8961	$92.90	$92.90	$92.90
Purchase #6	$104.92	8.128%	$113.4479	$113.45	$113.45	$113.40
Purchase #7	$142.33	9.790%	$156.2641	$156.26	$156.25	$156.30
7 purchase totals =	$638.16		$700.8926	$700.90	$700.90	$700.90