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	$53.36	6.224%	$56.6811	$56.68	$56.70	$56.70
Purchase #2	$80.89	11.798%	$90.4334	$90.43	$90.45	$90.40
Purchase #3	$93.73	10.197%	$103.2876	$103.29	$103.30	$103.30
Purchase #4	$66.46	4.635%	$69.5404	$69.54	$69.55	$69.50
Purchase #5	$166.78	4.868%	$174.8989	$174.90	$174.90	$174.90
Purchase #6	$213.94	7.661%	$230.3299	$230.33	$230.35	$230.30
Purchase #7	$20.46	4.702%	$21.422	$21.42	$21.40	$21.40
7 purchase totals =	$695.62		$746.5933	$746.59	$746.65	$746.50