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	$101.61	7.864%	$109.6006	$109.60	$109.60	$109.60
Purchase #2	$106.94	10.786%	$118.4745	$118.47	$118.45	$118.50
Purchase #3	$112.65	5.229%	$118.5405	$118.54	$118.55	$118.50
Purchase #4	$44.73	13.598%	$50.8124	$50.81	$50.80	$50.80
Purchase #5	$63.36	6.133%	$67.2459	$67.25	$67.25	$67.20
Purchase #6	$185.97	12.144%	$208.5542	$208.55	$208.55	$208.60
Purchase #7	$120.76	10.409%	$133.3299	$133.33	$133.35	$133.30
7 purchase totals =	$736.02		$806.5580	$806.55	$806.55	$806.50