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	$47.94	7.491%	$51.5312	$51.53	$51.55	$51.50
Purchase #2	$126.79	9.753%	$139.1558	$139.16	$139.15	$139.20
Purchase #3	$80.65	3.505%	$83.4768	$83.48	$83.50	$83.50
Purchase #4	$100.72	12.215%	$113.0229	$113.02	$113.00	$113.00
Purchase #5	$191.46	4.594%	$200.2557	$200.26	$200.25	$200.30
Purchase #6	$72.35	8.661%	$78.6162	$78.62	$78.60	$78.60
Purchase #7	$23.97	4.598%	$25.0721	$25.07	$25.05	$25.10
7 purchase totals =	$643.88		$691.1307	$691.14	$691.10	$691.20