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	$35.91	5.609%	$37.9242	$37.92	$37.90	$37.90
Purchase #2	$39.89	13.773%	$45.384	$45.38	$45.40	$45.40
Purchase #3	$140.34	5.316%	$147.8005	$147.80	$147.80	$147.80
Purchase #4	$240.26	7.379%	$257.9888	$257.99	$258.00	$258.00
Purchase #5	$175.65	10.601%	$194.2707	$194.27	$194.25	$194.30
Purchase #6	$15.61	12.787%	$17.6061	$17.61	$17.60	$17.60
Purchase #7	$90.64	9.333%	$99.0994	$99.10	$99.10	$99.10
7 purchase totals =	$738.30		$800.0737	$800.07	$800.05	$800.10