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	$124.32	3.670%	$128.8825	$128.88	$128.90	$128.90
Purchase #2	$118.41	3.774%	$122.8788	$122.88	$122.90	$122.90
Purchase #3	$138.79	6.668%	$148.0445	$148.04	$148.05	$148.00
Purchase #4	$196.35	8.243%	$212.5351	$212.54	$212.55	$212.50
Purchase #5	$122.69	12.301%	$137.7821	$137.78	$137.80	$137.80
Purchase #6	$29.93	7.698%	$32.234	$32.23	$32.25	$32.20
Purchase #7	$137.40	10.195%	$151.4079	$151.41	$151.40	$151.40
7 purchase totals =	$867.89		$933.7649	$933.76	$933.85	$933.70