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	$37.50	4.164%	$39.0615	$39.06	$39.05	$39.10
Purchase #2	$38.29	11.249%	$42.5972	$42.60	$42.60	$42.60
Purchase #3	$187.62	9.528%	$205.4964	$205.50	$205.50	$205.50
Purchase #4	$165.30	12.280%	$185.5988	$185.60	$185.60	$185.60
Purchase #5	$249.34	10.604%	$275.78	$275.78	$275.80	$275.80
Purchase #6	$136.65	7.530%	$146.9397	$146.94	$146.95	$146.90
Purchase #7	$7.50	9.151%	$8.1863	$8.19	$8.20	$8.20
7 purchase totals =	$822.20		$903.6599	$903.67	$903.70	$903.70