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	$72.97	3.141%	$75.262	$75.26	$75.25	$75.30
Purchase #2	$223.85	9.801%	$245.7895	$245.79	$245.80	$245.80
Purchase #3	$64.76	11.558%	$72.245	$72.25	$72.25	$72.20
Purchase #4	$95.77	7.575%	$103.0246	$103.02	$103.00	$103.00
Purchase #5	$64.91	10.247%	$71.5613	$71.56	$71.55	$71.60
Purchase #6	$41.70	4.201%	$43.4518	$43.45	$43.45	$43.50
Purchase #7	$18.91	11.535%	$21.0913	$21.09	$21.10	$21.10
7 purchase totals =	$582.87		$632.4255	$632.42	$632.40	$632.50