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	$203.82	11.622%	$227.508	$227.51	$227.50	$227.50
Purchase #2	$222.39	11.232%	$247.3688	$247.37	$247.35	$247.40
Purchase #3	$64.40	6.113%	$68.3368	$68.34	$68.35	$68.30
Purchase #4	$144.27	5.579%	$152.3188	$152.32	$152.30	$152.30
Purchase #5	$71.67	12.196%	$80.4109	$80.41	$80.40	$80.40
Purchase #6	$65.89	8.314%	$71.3681	$71.37	$71.35	$71.40
Purchase #7	$141.85	7.403%	$152.3512	$152.35	$152.35	$152.40
7 purchase totals =	$914.29		$999.6626	$999.67	$999.60	$999.70