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	$114.35	7.604%	$123.0452	$123.05	$123.05	$123.00
Purchase #2	$36.63	9.568%	$40.1348	$40.13	$40.15	$40.10
Purchase #3	$205.29	13.242%	$232.4745	$232.47	$232.45	$232.50
Purchase #4	$13.44	11.439%	$14.9774	$14.98	$15.00	$15.00
Purchase #5	$148.59	12.647%	$167.3822	$167.38	$167.40	$167.40
Purchase #6	$159.70	3.788%	$165.7494	$165.75	$165.75	$165.70
Purchase #7	$39.85	13.705%	$45.3114	$45.31	$45.30	$45.30
7 purchase totals =	$717.85		$789.0749	$789.07	$789.10	$789.00