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	$27.57	6.651%	$29.4037	$29.40	$29.40	$29.40
Purchase #2	$40.77	5.716%	$43.1004	$43.10	$43.10	$43.10
Purchase #3	$204.42	5.413%	$215.4853	$215.49	$215.50	$215.50
Purchase #4	$214.81	12.199%	$241.0147	$241.01	$241.00	$241.00
Purchase #5	$217.74	11.699%	$243.2134	$243.21	$243.20	$243.20
Purchase #6	$183.63	9.386%	$200.8655	$200.87	$200.85	$200.90
Purchase #7	$34.38	7.617%	$36.9987	$37.00	$37.00	$37.00
7 purchase totals =	$923.32		$1,010.0817	$1,010.08	$1,010.05	$1,010.10