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	$6.54	4.728%	$6.8492	$6.85	$6.85	$6.80
Purchase #2	$94.69	5.778%	$100.1612	$100.16	$100.15	$100.20
Purchase #3	$233.69	4.157%	$243.4045	$243.40	$243.40	$243.40
Purchase #4	$92.40	8.695%	$100.4342	$100.43	$100.45	$100.40
Purchase #5	$90.72	10.266%	$100.0333	$100.03	$100.05	$100.00
Purchase #6	$30.30	9.853%	$33.2855	$33.29	$33.30	$33.30
Purchase #7	$207.32	13.392%	$235.0843	$235.08	$235.10	$235.10
7 purchase totals =	$755.66		$819.2522	$819.24	$819.30	$819.20