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	$248.84	10.674%	$275.4012	$275.40	$275.40	$275.40
Purchase #2	$191.83	12.562%	$215.9277	$215.93	$215.95	$215.90
Purchase #3	$11.77	12.870%	$13.2848	$13.28	$13.30	$13.30
Purchase #4	$101.51	3.748%	$105.3146	$105.31	$105.30	$105.30
Purchase #5	$97.28	6.281%	$103.3902	$103.39	$103.40	$103.40
Purchase #6	$32.25	13.770%	$36.6908	$36.69	$36.70	$36.70
Purchase #7	$31.60	9.488%	$34.5982	$34.60	$34.60	$34.60
7 purchase totals =	$715.08		$784.6075	$784.60	$784.65	$784.60