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	$25.26	10.862%	$28.0037	$28.00	$28.00	$28.00
Purchase #2	$48.59	3.610%	$50.3441	$50.34	$50.35	$50.30
Purchase #3	$125.68	13.161%	$142.2207	$142.22	$142.20	$142.20
Purchase #4	$120.70	5.658%	$127.5292	$127.53	$127.55	$127.50
Purchase #5	$33.53	7.221%	$35.9512	$35.95	$35.95	$36.00
Purchase #6	$25.91	9.486%	$28.3678	$28.37	$28.35	$28.40
Purchase #7	$245.37	11.188%	$272.822	$272.82	$272.80	$272.80
7 purchase totals =	$625.04		$685.2387	$685.23	$685.20	$685.20