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	$166.43	12.254%	$186.8243	$186.82	$186.80	$186.80
Purchase #2	$139.79	13.830%	$159.123	$159.12	$159.10	$159.10
Purchase #3	$137.48	6.589%	$146.5386	$146.54	$146.55	$146.50
Purchase #4	$98.40	7.375%	$105.657	$105.66	$105.65	$105.70
Purchase #5	$98.88	6.735%	$105.5396	$105.54	$105.55	$105.50
Purchase #6	$16.73	3.394%	$17.2978	$17.30	$17.30	$17.30
Purchase #7	$158.29	5.189%	$166.5037	$166.50	$166.50	$166.50
7 purchase totals =	$816.00		$887.4840	$887.48	$887.45	$887.40