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	$79.97	12.205%	$89.7303	$89.73	$89.75	$89.70
Purchase #2	$91.48	13.514%	$103.8426	$103.84	$103.85	$103.80
Purchase #3	$160.84	9.868%	$176.7117	$176.71	$176.70	$176.70
Purchase #4	$107.49	8.366%	$116.4826	$116.48	$116.50	$116.50
Purchase #5	$247.86	11.847%	$277.224	$277.22	$277.20	$277.20
Purchase #6	$169.98	7.445%	$182.635	$182.64	$182.65	$182.60
Purchase #7	$79.45	12.714%	$89.5513	$89.55	$89.55	$89.60
7 purchase totals =	$937.07		$1,036.1775	$1,036.17	$1,036.20	$1,036.10