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	$29.69	8.498%	$32.2131	$32.21	$32.20	$32.20
Purchase #2	$78.57	10.293%	$86.6572	$86.66	$86.65	$86.70
Purchase #3	$211.77	8.856%	$230.5244	$230.52	$230.50	$230.50
Purchase #4	$143.38	4.686%	$150.0988	$150.10	$150.10	$150.10
Purchase #5	$65.47	10.350%	$72.2461	$72.25	$72.25	$72.20
Purchase #6	$34.36	9.218%	$37.5273	$37.53	$37.55	$37.50
Purchase #7	$156.48	12.747%	$176.4265	$176.43	$176.45	$176.40
7 purchase totals =	$719.72		$785.6934	$785.70	$785.70	$785.60