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	$49.32	10.300%	$54.4	$54.40	$54.40	$54.40
Purchase #2	$174.79	8.127%	$188.9952	$189.00	$189.00	$189.00
Purchase #3	$46.78	7.845%	$50.4499	$50.45	$50.45	$50.40
Purchase #4	$246.45	12.764%	$277.9069	$277.91	$277.90	$277.90
Purchase #5	$95.75	9.545%	$104.8893	$104.89	$104.90	$104.90
Purchase #6	$17.75	3.456%	$18.3634	$18.36	$18.35	$18.40
Purchase #7	$84.69	7.372%	$90.9333	$90.93	$90.95	$90.90
7 purchase totals =	$715.53		$785.9380	$785.94	$785.95	$785.90