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	$99.83	12.105%	$111.9144	$111.91	$111.90	$111.90
Purchase #2	$176.93	7.739%	$190.6226	$190.62	$190.60	$190.60
Purchase #3	$47.69	7.652%	$51.3392	$51.34	$51.35	$51.30
Purchase #4	$54.75	3.642%	$56.744	$56.74	$56.75	$56.70
Purchase #5	$189.86	11.166%	$211.0598	$211.06	$211.05	$211.10
Purchase #6	$20.41	9.787%	$22.4075	$22.41	$22.40	$22.40
Purchase #7	$39.63	4.284%	$41.3277	$41.33	$41.35	$41.30
7 purchase totals =	$629.10		$685.4152	$685.41	$685.40	$685.30