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	$84.60	7.568%	$91.0025	$91.00	$91.00	$91.00
Purchase #2	$134.45	11.607%	$150.0556	$150.06	$150.05	$150.10
Purchase #3	$20.43	4.329%	$21.3144	$21.31	$21.30	$21.30
Purchase #4	$145.47	4.857%	$152.5355	$152.54	$152.55	$152.50
Purchase #5	$63.74	4.129%	$66.3718	$66.37	$66.35	$66.40
Purchase #6	$209.57	12.150%	$235.0328	$235.03	$235.05	$235.00
Purchase #7	$11.51	3.169%	$11.8748	$11.87	$11.85	$11.90
7 purchase totals =	$669.77		$728.1874	$728.18	$728.15	$728.20