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	$134.86	8.558%	$146.4013	$146.40	$146.40	$146.40
Purchase #2	$138.72	12.182%	$155.6189	$155.62	$155.60	$155.60
Purchase #3	$90.36	8.564%	$98.0984	$98.10	$98.10	$98.10
Purchase #4	$183.55	5.863%	$194.3115	$194.31	$194.30	$194.30
Purchase #5	$63.74	6.544%	$67.9111	$67.91	$67.90	$67.90
Purchase #6	$38.80	4.578%	$40.5763	$40.58	$40.60	$40.60
Purchase #7	$104.31	8.283%	$112.95	$112.95	$112.95	$113.00
7 purchase totals =	$754.34		$815.8675	$815.87	$815.85	$815.90