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	$79.30	13.435%	$89.954	$89.95	$89.95	$90.00
Purchase #2	$52.86	4.861%	$55.4295	$55.43	$55.45	$55.40
Purchase #3	$43.58	8.484%	$47.2773	$47.28	$47.30	$47.30
Purchase #4	$162.78	9.507%	$178.2555	$178.26	$178.25	$178.30
Purchase #5	$113.47	13.410%	$128.6863	$128.69	$128.70	$128.70
Purchase #6	$61.72	13.375%	$69.9751	$69.98	$70.00	$70.00
Purchase #7	$126.32	12.317%	$141.8788	$141.88	$141.90	$141.90
7 purchase totals =	$640.03		$711.4565	$711.47	$711.55	$711.60