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	$38.38	10.425%	$42.3811	$42.38	$42.40	$42.40
Purchase #2	$18.73	4.336%	$19.5421	$19.54	$19.55	$19.50
Purchase #3	$215.27	4.802%	$225.6073	$225.61	$225.60	$225.60
Purchase #4	$152.58	13.610%	$173.3461	$173.35	$173.35	$173.30
Purchase #5	$110.84	4.204%	$115.4997	$115.50	$115.50	$115.50
Purchase #6	$171.45	11.154%	$190.5735	$190.57	$190.55	$190.60
Purchase #7	$184.94	5.775%	$195.6203	$195.62	$195.60	$195.60
7 purchase totals =	$892.19		$962.5701	$962.57	$962.55	$962.50