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	$95.43	5.190%	$100.3828	$100.38	$100.40	$100.40
Purchase #2	$179.48	9.665%	$196.8267	$196.83	$196.85	$196.80
Purchase #3	$250.25	9.257%	$273.4156	$273.42	$273.40	$273.40
Purchase #4	$9.97	4.435%	$10.4122	$10.41	$10.40	$10.40
Purchase #5	$245.74	6.497%	$261.7057	$261.71	$261.70	$261.70
Purchase #6	$245.37	8.705%	$266.7295	$266.73	$266.75	$266.70
Purchase #7	$237.99	12.407%	$267.5174	$267.52	$267.50	$267.50
7 purchase totals =	$1,264.23		$1,376.9899	$1,377.00	$1,377.00	$1,376.90