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	$84.51	6.539%	$90.0361	$90.04	$90.05	$90.00
Purchase #2	$86.97	4.238%	$90.6558	$90.66	$90.65	$90.70
Purchase #3	$225.93	4.244%	$235.5185	$235.52	$235.50	$235.50
Purchase #4	$141.83	6.816%	$151.4971	$151.50	$151.50	$151.50
Purchase #5	$71.93	9.322%	$78.6353	$78.64	$78.65	$78.60
Purchase #6	$250.58	10.327%	$276.4574	$276.46	$276.45	$276.50
Purchase #7	$98.74	10.256%	$108.8668	$108.87	$108.85	$108.90
7 purchase totals =	$960.49		$1,031.6670	$1,031.69	$1,031.65	$1,031.70