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	$55.89	8.461%	$60.6189	$60.62	$60.60	$60.60
Purchase #2	$85.72	10.664%	$94.8612	$94.86	$94.85	$94.90
Purchase #3	$246.64	5.232%	$259.5442	$259.54	$259.55	$259.50
Purchase #4	$228.79	13.536%	$259.759	$259.76	$259.75	$259.80
Purchase #5	$110.79	11.820%	$123.8854	$123.89	$123.90	$123.90
Purchase #6	$139.85	10.745%	$154.8769	$154.88	$154.90	$154.90
Purchase #7	$158.40	13.723%	$180.1372	$180.14	$180.15	$180.10
7 purchase totals =	$1,026.08		$1,133.6828	$1,133.69	$1,133.70	$1,133.70