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	$75.57	8.857%	$82.2632	$82.26	$82.25	$82.30
Purchase #2	$118.67	13.696%	$134.923	$134.92	$134.90	$134.90
Purchase #3	$103.40	9.136%	$112.8466	$112.85	$112.85	$112.80
Purchase #4	$141.77	10.258%	$156.3128	$156.31	$156.30	$156.30
Purchase #5	$19.70	8.579%	$21.3901	$21.39	$21.40	$21.40
Purchase #6	$171.65	7.136%	$183.8989	$183.90	$183.90	$183.90
Purchase #7	$104.45	11.155%	$116.1014	$116.10	$116.10	$116.10
7 purchase totals =	$735.21		$807.7360	$807.73	$807.70	$807.70