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	$128.83	6.761%	$137.5402	$137.54	$137.55	$137.50
Purchase #2	$51.61	13.677%	$58.6687	$58.67	$58.65	$58.70
Purchase #3	$106.92	12.165%	$119.9268	$119.93	$119.95	$119.90
Purchase #4	$47.85	4.788%	$50.1411	$50.14	$50.15	$50.10
Purchase #5	$29.55	10.329%	$32.6022	$32.60	$32.60	$32.60
Purchase #6	$103.59	6.140%	$109.9504	$109.95	$109.95	$110.00
Purchase #7	$238.99	7.116%	$255.9965	$256.00	$256.00	$256.00
7 purchase totals =	$707.34		$764.8259	$764.83	$764.85	$764.80