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	$80.30	10.268%	$88.5452	$88.55	$88.55	$88.50
Purchase #2	$43.61	8.508%	$47.3203	$47.32	$47.30	$47.30
Purchase #3	$80.74	12.172%	$90.5677	$90.57	$90.55	$90.60
Purchase #4	$37.97	10.366%	$41.906	$41.91	$41.90	$41.90
Purchase #5	$216.95	3.286%	$224.079	$224.08	$224.10	$224.10
Purchase #6	$32.66	12.470%	$36.7327	$36.73	$36.75	$36.70
Purchase #7	$167.32	13.650%	$190.1592	$190.16	$190.15	$190.20
7 purchase totals =	$659.55		$719.3101	$719.32	$719.30	$719.30