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	$129.97	7.841%	$140.1609	$140.16	$140.15	$140.20
Purchase #2	$49.92	12.667%	$56.2434	$56.24	$56.25	$56.20
Purchase #3	$184.47	6.637%	$196.7133	$196.71	$196.70	$196.70
Purchase #4	$39.67	10.869%	$43.9817	$43.98	$44.00	$44.00
Purchase #5	$20.89	12.317%	$23.463	$23.46	$23.45	$23.50
Purchase #6	$115.64	13.672%	$131.4503	$131.45	$131.45	$131.50
Purchase #7	$150.33	3.269%	$155.2443	$155.24	$155.25	$155.20
7 purchase totals =	$690.89		$747.2569	$747.24	$747.25	$747.30