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	$185.95	10.513%	$205.4989	$205.50	$205.50	$205.50
Purchase #2	$20.36	7.218%	$21.8296	$21.83	$21.85	$21.80
Purchase #3	$244.81	13.186%	$277.0906	$277.09	$277.10	$277.10
Purchase #4	$106.75	6.415%	$113.598	$113.60	$113.60	$113.60
Purchase #5	$52.64	3.639%	$54.5556	$54.56	$54.55	$54.60
Purchase #6	$151.32	13.275%	$171.4077	$171.41	$171.40	$171.40
Purchase #7	$18.59	12.304%	$20.8773	$20.88	$20.90	$20.90
7 purchase totals =	$780.42		$864.8577	$864.87	$864.90	$864.90