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	$166.91	12.126%	$187.1495	$187.15	$187.15	$187.10
Purchase #2	$59.41	13.533%	$67.45	$67.45	$67.45	$67.50
Purchase #3	$172.66	8.229%	$186.8682	$186.87	$186.85	$186.90
Purchase #4	$81.93	10.173%	$90.2647	$90.26	$90.25	$90.30
Purchase #5	$97.85	7.874%	$105.5547	$105.55	$105.55	$105.60
Purchase #6	$32.81	13.816%	$37.343	$37.34	$37.35	$37.30
Purchase #7	$130.86	12.575%	$147.3156	$147.32	$147.30	$147.30
7 purchase totals =	$742.43		$821.9457	$821.94	$821.90	$822.00