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	$135.96	4.140%	$141.5887	$141.59	$141.60	$141.60
Purchase #2	$50.56	12.467%	$56.8633	$56.86	$56.85	$56.90
Purchase #3	$209.62	7.273%	$224.8657	$224.87	$224.85	$224.90
Purchase #4	$106.64	8.397%	$115.5946	$115.59	$115.60	$115.60
Purchase #5	$108.77	3.355%	$112.4192	$112.42	$112.40	$112.40
Purchase #6	$46.32	10.645%	$51.2508	$51.25	$51.25	$51.30
Purchase #7	$87.77	13.165%	$99.3249	$99.32	$99.30	$99.30
7 purchase totals =	$745.64		$801.9072	$801.90	$801.85	$802.00