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	$250.75	11.492%	$279.5662	$279.57	$279.55	$279.60
Purchase #2	$57.85	10.673%	$64.0243	$64.02	$64.00	$64.00
Purchase #3	$221.88	13.108%	$250.964	$250.96	$250.95	$251.00
Purchase #4	$70.42	11.839%	$78.757	$78.76	$78.75	$78.80
Purchase #5	$10.53	9.848%	$11.567	$11.57	$11.55	$11.60
Purchase #6	$134.32	12.285%	$150.8212	$150.82	$150.80	$150.80
Purchase #7	$67.99	10.106%	$74.8611	$74.86	$74.85	$74.90
7 purchase totals =	$813.74		$910.5608	$910.56	$910.45	$910.70