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	$25.70	4.589%	$26.8794	$26.88	$26.90	$26.90
Purchase #2	$68.91	11.835%	$77.0655	$77.07	$77.05	$77.10
Purchase #3	$42.78	6.300%	$45.4751	$45.48	$45.50	$45.50
Purchase #4	$99.98	8.296%	$108.2743	$108.27	$108.25	$108.30
Purchase #5	$133.65	9.352%	$146.1489	$146.15	$146.15	$146.10
Purchase #6	$21.85	12.212%	$24.5183	$24.52	$24.50	$24.50
Purchase #7	$38.85	5.185%	$40.8644	$40.86	$40.85	$40.90
7 purchase totals =	$431.72		$469.2259	$469.23	$469.20	$469.30