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	$19.50	7.231%	$20.91	$20.91	$20.90	$20.90
Purchase #2	$16.91	8.435%	$18.3364	$18.34	$18.35	$18.30
Purchase #3	$229.78	5.429%	$242.2548	$242.25	$242.25	$242.30
Purchase #4	$40.30	10.865%	$44.6786	$44.68	$44.70	$44.70
Purchase #5	$124.88	11.196%	$138.8616	$138.86	$138.85	$138.90
Purchase #6	$156.99	9.227%	$171.4755	$171.48	$171.50	$171.50
Purchase #7	$115.54	6.791%	$123.3863	$123.39	$123.40	$123.40
7 purchase totals =	$703.90		$759.9032	$759.91	$759.95	$760.00