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	$133.87	13.286%	$151.656	$151.66	$151.65	$151.70
Purchase #2	$137.46	9.681%	$150.7675	$150.77	$150.75	$150.80
Purchase #3	$219.97	9.494%	$240.854	$240.85	$240.85	$240.90
Purchase #4	$65.95	10.204%	$72.6795	$72.68	$72.70	$72.70
Purchase #5	$197.59	12.621%	$222.5278	$222.53	$222.55	$222.50
Purchase #6	$218.43	3.522%	$226.1231	$226.12	$226.10	$226.10
Purchase #7	$75.62	3.727%	$78.4384	$78.44	$78.45	$78.40
7 purchase totals =	$1,048.89		$1,143.0463	$1,143.05	$1,143.05	$1,143.10