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	$199.96	7.373%	$214.7031	$214.70	$214.70	$214.70
Purchase #2	$218.86	5.158%	$230.1488	$230.15	$230.15	$230.10
Purchase #3	$130.78	7.698%	$140.8474	$140.85	$140.85	$140.80
Purchase #4	$81.33	10.618%	$89.9656	$89.97	$89.95	$90.00
Purchase #5	$87.72	3.486%	$90.7779	$90.78	$90.80	$90.80
Purchase #6	$38.92	11.377%	$43.3479	$43.35	$43.35	$43.30
Purchase #7	$71.95	12.648%	$81.0502	$81.05	$81.05	$81.10
7 purchase totals =	$829.52		$890.8409	$890.85	$890.85	$890.80