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	$24.75	12.156%	$27.7586	$27.76	$27.75	$27.80
Purchase #2	$158.73	9.120%	$173.2062	$173.21	$173.20	$173.20
Purchase #3	$41.90	9.395%	$45.8365	$45.84	$45.85	$45.80
Purchase #4	$154.93	9.334%	$169.3912	$169.39	$169.40	$169.40
Purchase #5	$61.92	3.874%	$64.3188	$64.32	$64.30	$64.30
Purchase #6	$76.38	13.756%	$86.8868	$86.89	$86.90	$86.90
Purchase #7	$54.93	13.770%	$62.4939	$62.49	$62.50	$62.50
7 purchase totals =	$573.54		$629.8920	$629.90	$629.90	$629.90