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	$63.26	11.501%	$70.5355	$70.54	$70.55	$70.50
Purchase #2	$231.32	10.177%	$254.8614	$254.86	$254.85	$254.90
Purchase #3	$92.86	13.406%	$105.3088	$105.31	$105.30	$105.30
Purchase #4	$208.85	6.628%	$222.6926	$222.69	$222.70	$222.70
Purchase #5	$187.92	12.401%	$211.224	$211.22	$211.20	$211.20
Purchase #6	$71.55	11.470%	$79.7568	$79.76	$79.75	$79.80
Purchase #7	$127.83	3.254%	$131.9896	$131.99	$132.00	$132.00
7 purchase totals =	$983.59		$1,076.3687	$1,076.37	$1,076.35	$1,076.40