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	$227.69	13.477%	$258.3758	$258.38	$258.40	$258.40
Purchase #2	$105.33	7.608%	$113.3435	$113.34	$113.35	$113.30
Purchase #3	$150.34	13.812%	$171.105	$171.11	$171.10	$171.10
Purchase #4	$144.52	4.397%	$150.8745	$150.87	$150.85	$150.90
Purchase #5	$106.71	13.655%	$121.2813	$121.28	$121.30	$121.30
Purchase #6	$159.78	11.730%	$178.5222	$178.52	$178.50	$178.50
Purchase #7	$11.80	4.393%	$12.3184	$12.32	$12.30	$12.30
7 purchase totals =	$906.17		$1,005.8207	$1,005.82	$1,005.80	$1,005.80