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	$240.57	6.136%	$255.3314	$255.33	$255.35	$255.30
Purchase #2	$169.69	4.757%	$177.7622	$177.76	$177.75	$177.80
Purchase #3	$92.70	12.175%	$103.9862	$103.99	$104.00	$104.00
Purchase #4	$122.38	11.413%	$136.3472	$136.35	$136.35	$136.30
Purchase #5	$119.76	6.308%	$127.3145	$127.31	$127.30	$127.30
Purchase #6	$195.32	13.764%	$222.2038	$222.20	$222.20	$222.20
Purchase #7	$170.59	11.176%	$189.6551	$189.66	$189.65	$189.70
7 purchase totals =	$1,111.01		$1,212.6004	$1,212.60	$1,212.60	$1,212.60