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	$141.43	6.391%	$150.4688	$150.47	$150.45	$150.50
Purchase #2	$153.94	8.152%	$166.4892	$166.49	$166.50	$166.50
Purchase #3	$250.67	10.281%	$276.4414	$276.44	$276.45	$276.40
Purchase #4	$241.44	13.289%	$273.525	$273.53	$273.55	$273.50
Purchase #5	$108.26	9.647%	$118.7038	$118.70	$118.70	$118.70
Purchase #6	$50.54	9.756%	$55.4707	$55.47	$55.45	$55.50
Purchase #7	$54.87	6.621%	$58.5029	$58.50	$58.50	$58.50
7 purchase totals =	$1,001.15		$1,099.6018	$1,099.60	$1,099.60	$1,099.60