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	$17.59	12.454%	$19.7807	$19.78	$19.80	$19.80
Purchase #2	$34.84	5.112%	$36.621	$36.62	$36.60	$36.60
Purchase #3	$185.73	13.169%	$210.1888	$210.19	$210.20	$210.20
Purchase #4	$126.88	9.813%	$139.3307	$139.33	$139.35	$139.30
Purchase #5	$126.85	3.320%	$131.0614	$131.06	$131.05	$131.10
Purchase #6	$159.60	7.440%	$171.4742	$171.47	$171.45	$171.50
Purchase #7	$48.59	8.706%	$52.8202	$52.82	$52.80	$52.80
7 purchase totals =	$700.08		$761.2770	$761.27	$761.25	$761.30