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	$239.47	11.357%	$266.6666	$266.67	$266.65	$266.70
Purchase #2	$113.54	6.446%	$120.8588	$120.86	$120.85	$120.90
Purchase #3	$96.92	6.568%	$103.2857	$103.29	$103.30	$103.30
Purchase #4	$100.28	4.682%	$104.9751	$104.98	$105.00	$105.00
Purchase #5	$15.32	3.450%	$15.8485	$15.85	$15.85	$15.80
Purchase #6	$77.69	7.601%	$83.5952	$83.60	$83.60	$83.60
Purchase #7	$138.63	4.758%	$145.226	$145.23	$145.25	$145.20
7 purchase totals =	$781.85		$840.4559	$840.48	$840.50	$840.50