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	$50.57	12.165%	$56.7218	$56.72	$56.70	$56.70
Purchase #2	$230.71	10.701%	$255.3983	$255.40	$255.40	$255.40
Purchase #3	$12.36	4.590%	$12.9273	$12.93	$12.95	$12.90
Purchase #4	$31.89	3.234%	$32.9213	$32.92	$32.90	$32.90
Purchase #5	$85.91	5.409%	$90.5569	$90.56	$90.55	$90.60
Purchase #6	$141.97	10.456%	$156.8144	$156.81	$156.80	$156.80
Purchase #7	$109.55	5.480%	$115.5533	$115.55	$115.55	$115.60
7 purchase totals =	$662.96		$720.8933	$720.89	$720.85	$720.90