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	$204.46	13.269%	$231.5898	$231.59	$231.60	$231.60
Purchase #2	$97.32	8.689%	$105.7761	$105.78	$105.80	$105.80
Purchase #3	$170.76	9.477%	$186.9429	$186.94	$186.95	$186.90
Purchase #4	$127.28	5.450%	$134.2168	$134.22	$134.20	$134.20
Purchase #5	$95.70	10.122%	$105.3868	$105.39	$105.40	$105.40
Purchase #6	$201.81	9.124%	$220.2231	$220.22	$220.20	$220.20
Purchase #7	$30.36	7.107%	$32.5177	$32.52	$32.50	$32.50
7 purchase totals =	$927.69		$1,016.6532	$1,016.66	$1,016.65	$1,016.60