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	$58.72	13.520%	$66.6589	$66.66	$66.65	$66.70
Purchase #2	$156.69	6.781%	$167.3151	$167.32	$167.30	$167.30
Purchase #3	$155.70	6.160%	$165.2911	$165.29	$165.30	$165.30
Purchase #4	$74.66	11.517%	$83.2586	$83.26	$83.25	$83.30
Purchase #5	$144.92	13.576%	$164.5943	$164.59	$164.60	$164.60
Purchase #6	$89.27	10.160%	$98.3398	$98.34	$98.35	$98.30
Purchase #7	$212.82	3.535%	$220.3432	$220.34	$220.35	$220.30
7 purchase totals =	$892.78		$965.8010	$965.80	$965.80	$965.80