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	$108.87	13.782%	$123.8745	$123.87	$123.85	$123.90
Purchase #2	$243.85	4.755%	$255.4451	$255.45	$255.45	$255.40
Purchase #3	$112.41	11.657%	$125.5136	$125.51	$125.50	$125.50
Purchase #4	$114.91	3.224%	$118.6147	$118.61	$118.60	$118.60
Purchase #5	$176.28	3.587%	$182.6032	$182.60	$182.60	$182.60
Purchase #6	$196.44	8.160%	$212.4695	$212.47	$212.45	$212.50
Purchase #7	$19.96	7.171%	$21.3913	$21.39	$21.40	$21.40
7 purchase totals =	$972.72		$1,039.9119	$1,039.90	$1,039.85	$1,039.90