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	$6.62	13.152%	$7.4907	$7.49	$7.50	$7.50
Purchase #2	$133.74	3.109%	$137.898	$137.90	$137.90	$137.90
Purchase #3	$95.65	4.234%	$99.6998	$99.70	$99.70	$99.70
Purchase #4	$132.91	7.548%	$142.942	$142.94	$142.95	$142.90
Purchase #5	$152.54	11.182%	$169.597	$169.60	$169.60	$169.60
Purchase #6	$22.69	12.547%	$25.5369	$25.54	$25.55	$25.50
Purchase #7	$142.85	7.284%	$153.2552	$153.26	$153.25	$153.30
7 purchase totals =	$687.00		$736.4196	$736.43	$736.45	$736.40