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	$139.91	13.686%	$159.0581	$159.06	$159.05	$159.10
Purchase #2	$106.65	4.603%	$111.5591	$111.56	$111.55	$111.60
Purchase #3	$5.79	11.331%	$6.4461	$6.45	$6.45	$6.40
Purchase #4	$172.57	7.744%	$185.9338	$185.93	$185.95	$185.90
Purchase #5	$132.52	8.349%	$143.5841	$143.58	$143.60	$143.60
Purchase #6	$92.39	13.665%	$105.0151	$105.02	$105.00	$105.00
Purchase #7	$189.78	11.123%	$210.8892	$210.89	$210.90	$210.90
7 purchase totals =	$839.61		$922.4855	$922.49	$922.50	$922.50