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	$246.59	10.260%	$271.8901	$271.89	$271.90	$271.90
Purchase #2	$78.91	8.461%	$85.5866	$85.59	$85.60	$85.60
Purchase #3	$185.58	4.683%	$194.2707	$194.27	$194.25	$194.30
Purchase #4	$221.25	7.869%	$238.6602	$238.66	$238.65	$238.70
Purchase #5	$108.90	7.377%	$116.9336	$116.93	$116.95	$116.90
Purchase #6	$193.46	12.822%	$218.2654	$218.27	$218.25	$218.30
Purchase #7	$145.76	11.652%	$162.744	$162.74	$162.75	$162.70
7 purchase totals =	$1,180.45		$1,288.3506	$1,288.35	$1,288.35	$1,288.40