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	$29.50	6.103%	$31.3004	$31.30	$31.30	$31.30
Purchase #2	$94.51	5.547%	$99.7525	$99.75	$99.75	$99.80
Purchase #3	$43.83	6.821%	$46.8196	$46.82	$46.80	$46.80
Purchase #4	$218.39	10.287%	$240.8558	$240.86	$240.85	$240.90
Purchase #5	$99.71	6.747%	$106.4374	$106.44	$106.45	$106.40
Purchase #6	$194.89	13.444%	$221.091	$221.09	$221.10	$221.10
Purchase #7	$213.79	3.848%	$222.0166	$222.02	$222.00	$222.00
7 purchase totals =	$894.62		$968.2733	$968.28	$968.25	$968.30