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	$124.41	10.556%	$137.5427	$137.54	$137.55	$137.50
Purchase #2	$173.63	8.545%	$188.4667	$188.47	$188.45	$188.50
Purchase #3	$141.57	12.264%	$158.9321	$158.93	$158.95	$158.90
Purchase #4	$135.71	12.569%	$152.7674	$152.77	$152.75	$152.80
Purchase #5	$79.56	7.872%	$85.823	$85.82	$85.80	$85.80
Purchase #6	$214.96	10.256%	$237.0063	$237.01	$237.00	$237.00
Purchase #7	$244.77	4.257%	$255.1899	$255.19	$255.20	$255.20
7 purchase totals =	$1,114.61		$1,215.7281	$1,215.73	$1,215.70	$1,215.70