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	$134.71	8.534%	$146.2062	$146.21	$146.20	$146.20
Purchase #2	$91.69	8.851%	$99.8055	$99.81	$99.80	$99.80
Purchase #3	$215.53	12.458%	$242.3807	$242.38	$242.40	$242.40
Purchase #4	$104.80	5.357%	$110.4141	$110.41	$110.40	$110.40
Purchase #5	$233.52	10.647%	$258.3829	$258.38	$258.40	$258.40
Purchase #6	$128.83	6.652%	$137.3998	$137.40	$137.40	$137.40
Purchase #7	$140.78	3.647%	$145.9142	$145.91	$145.90	$145.90
7 purchase totals =	$1,049.86		$1,140.5034	$1,140.50	$1,140.50	$1,140.50