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	$90.27	9.315%	$98.6787	$98.68	$98.70	$98.70
Purchase #2	$95.81	7.563%	$103.0561	$103.06	$103.05	$103.10
Purchase #3	$80.32	6.731%	$85.7263	$85.73	$85.75	$85.70
Purchase #4	$40.77	3.661%	$42.2626	$42.26	$42.25	$42.30
Purchase #5	$231.37	8.813%	$251.7606	$251.76	$251.75	$251.80
Purchase #6	$192.92	6.797%	$206.0328	$206.03	$206.05	$206.00
Purchase #7	$77.45	6.664%	$82.6113	$82.61	$82.60	$82.60
7 purchase totals =	$808.91		$870.1284	$870.13	$870.15	$870.20