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	$138.47	4.838%	$145.1692	$145.17	$145.15	$145.20
Purchase #2	$196.72	9.414%	$215.2392	$215.24	$215.25	$215.20
Purchase #3	$182.59	3.326%	$188.6629	$188.66	$188.65	$188.70
Purchase #4	$109.33	12.134%	$122.5961	$122.60	$122.60	$122.60
Purchase #5	$19.50	3.439%	$20.1706	$20.17	$20.15	$20.20
Purchase #6	$147.76	9.831%	$162.2863	$162.29	$162.30	$162.30
Purchase #7	$42.32	6.346%	$45.0056	$45.01	$45.00	$45.00
7 purchase totals =	$836.69		$899.1299	$899.14	$899.10	$899.20