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	$25.49	7.757%	$27.4673	$27.47	$27.45	$27.50
Purchase #2	$150.48	8.319%	$162.9984	$163.00	$163.00	$163.00
Purchase #3	$49.71	6.168%	$52.7761	$52.78	$52.80	$52.80
Purchase #4	$189.90	3.697%	$196.9206	$196.92	$196.90	$196.90
Purchase #5	$159.75	10.263%	$176.1451	$176.15	$176.15	$176.10
Purchase #6	$173.49	8.350%	$187.9764	$187.98	$188.00	$188.00
Purchase #7	$52.69	3.436%	$54.5004	$54.50	$54.50	$54.50
7 purchase totals =	$801.51		$858.7843	$858.80	$858.80	$858.80