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	$89.60	13.527%	$101.7202	$101.72	$101.70	$101.70
Purchase #2	$81.52	12.383%	$91.6146	$91.61	$91.60	$91.60
Purchase #3	$112.54	11.654%	$125.6554	$125.66	$125.65	$125.70
Purchase #4	$235.39	11.403%	$262.2315	$262.23	$262.25	$262.20
Purchase #5	$20.37	6.280%	$21.6492	$21.65	$21.65	$21.60
Purchase #6	$48.55	3.499%	$50.2488	$50.25	$50.25	$50.20
Purchase #7	$243.82	4.660%	$255.182	$255.18	$255.20	$255.20
7 purchase totals =	$831.79		$908.3017	$908.30	$908.30	$908.20