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	$24.94	3.392%	$25.786	$25.79	$25.80	$25.80
Purchase #2	$175.39	9.307%	$191.7135	$191.71	$191.70	$191.70
Purchase #3	$189.59	11.708%	$211.7872	$211.79	$211.80	$211.80
Purchase #4	$162.66	9.789%	$178.5828	$178.58	$178.60	$178.60
Purchase #5	$65.92	10.112%	$72.5858	$72.59	$72.60	$72.60
Purchase #6	$181.70	4.844%	$190.5015	$190.50	$190.50	$190.50
Purchase #7	$99.38	13.183%	$112.4813	$112.48	$112.50	$112.50
7 purchase totals =	$899.58		$983.4381	$983.44	$983.50	$983.50