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	$212.32	13.152%	$240.2443	$240.24	$240.25	$240.20
Purchase #2	$156.94	6.414%	$167.0061	$167.01	$167.00	$167.00
Purchase #3	$208.94	8.795%	$227.3163	$227.32	$227.30	$227.30
Purchase #4	$198.61	3.505%	$205.5713	$205.57	$205.55	$205.60
Purchase #5	$65.66	5.185%	$69.0645	$69.06	$69.05	$69.10
Purchase #6	$18.89	7.111%	$20.2333	$20.23	$20.25	$20.20
Purchase #7	$156.88	9.252%	$171.3945	$171.39	$171.40	$171.40
7 purchase totals =	$1,018.24		$1,100.8303	$1,100.82	$1,100.80	$1,100.80