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	$65.64	6.802%	$70.1048	$70.10	$70.10	$70.10
Purchase #2	$69.37	7.785%	$74.7705	$74.77	$74.75	$74.80
Purchase #3	$131.94	8.369%	$142.9821	$142.98	$143.00	$143.00
Purchase #4	$54.69	8.168%	$59.1571	$59.16	$59.15	$59.20
Purchase #5	$24.51	12.571%	$27.5912	$27.59	$27.60	$27.60
Purchase #6	$94.95	7.301%	$101.8823	$101.88	$101.90	$101.90
Purchase #7	$239.66	6.580%	$255.4296	$255.43	$255.45	$255.40
7 purchase totals =	$680.76		$731.9176	$731.91	$731.95	$732.00