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	$247.44	3.823%	$256.8996	$256.90	$256.90	$256.90
Purchase #2	$16.35	13.670%	$18.585	$18.59	$18.60	$18.60
Purchase #3	$108.39	3.353%	$112.0243	$112.02	$112.00	$112.00
Purchase #4	$93.80	7.463%	$100.8003	$100.80	$100.80	$100.80
Purchase #5	$240.84	9.426%	$263.5416	$263.54	$263.55	$263.50
Purchase #6	$139.94	12.459%	$157.3751	$157.38	$157.40	$157.40
Purchase #7	$118.87	10.585%	$131.4524	$131.45	$131.45	$131.50
7 purchase totals =	$965.63		$1,040.6783	$1,040.68	$1,040.70	$1,040.70