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	$99.77	3.243%	$103.0055	$103.01	$103.00	$103.00
Purchase #2	$248.93	7.382%	$267.306	$267.31	$267.30	$267.30
Purchase #3	$163.54	13.668%	$185.8926	$185.89	$185.90	$185.90
Purchase #4	$153.66	5.128%	$161.5397	$161.54	$161.55	$161.50
Purchase #5	$194.35	13.868%	$221.3025	$221.30	$221.30	$221.30
Purchase #6	$168.86	12.758%	$190.4032	$190.40	$190.40	$190.40
Purchase #7	$209.39	4.155%	$218.0902	$218.09	$218.10	$218.10
7 purchase totals =	$1,238.50		$1,347.5397	$1,347.54	$1,347.55	$1,347.50