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	$166.32	6.278%	$176.7616	$176.76	$176.75	$176.80
Purchase #2	$96.77	3.548%	$100.2034	$100.20	$100.20	$100.20
Purchase #3	$30.96	7.774%	$33.3668	$33.37	$33.35	$33.40
Purchase #4	$198.53	13.190%	$224.7161	$224.72	$224.70	$224.70
Purchase #5	$66.85	8.535%	$72.5556	$72.56	$72.55	$72.60
Purchase #6	$24.70	9.552%	$27.0593	$27.06	$27.05	$27.10
Purchase #7	$29.41	9.448%	$32.1887	$32.19	$32.20	$32.20
7 purchase totals =	$613.54		$666.8515	$666.86	$666.80	$667.00