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	$46.90	7.868%	$50.5901	$50.59	$50.60	$50.60
Purchase #2	$72.88	8.456%	$79.0427	$79.04	$79.05	$79.00
Purchase #3	$28.72	11.716%	$32.0848	$32.08	$32.10	$32.10
Purchase #4	$25.95	10.180%	$28.5917	$28.59	$28.60	$28.60
Purchase #5	$168.94	12.626%	$190.2704	$190.27	$190.25	$190.30
Purchase #6	$220.92	12.162%	$247.7883	$247.79	$247.80	$247.80
Purchase #7	$123.94	6.154%	$131.5673	$131.57	$131.55	$131.60
7 purchase totals =	$688.25		$759.9353	$759.93	$759.95	$760.00