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	$203.52	9.314%	$222.4759	$222.48	$222.50	$222.50
Purchase #2	$28.30	11.591%	$31.5803	$31.58	$31.60	$31.60
Purchase #3	$150.28	12.174%	$168.5751	$168.58	$168.60	$168.60
Purchase #4	$100.26	5.349%	$105.6229	$105.62	$105.60	$105.60
Purchase #5	$16.52	11.339%	$18.3932	$18.39	$18.40	$18.40
Purchase #6	$44.84	5.206%	$47.1744	$47.17	$47.15	$47.20
Purchase #7	$42.75	4.534%	$44.6883	$44.69	$44.70	$44.70
7 purchase totals =	$586.47		$638.5101	$638.51	$638.55	$638.60