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	$103.31	10.136%	$113.7815	$113.78	$113.80	$113.80
Purchase #2	$172.34	5.439%	$181.7136	$181.71	$181.70	$181.70
Purchase #3	$82.25	8.215%	$89.0068	$89.01	$89.00	$89.00
Purchase #4	$149.65	12.105%	$167.7651	$167.77	$167.75	$167.80
Purchase #5	$17.73	3.590%	$18.3665	$18.37	$18.35	$18.40
Purchase #6	$33.59	6.289%	$35.7025	$35.70	$35.70	$35.70
Purchase #7	$144.48	9.578%	$158.3183	$158.32	$158.30	$158.30
7 purchase totals =	$703.35		$764.6543	$764.66	$764.60	$764.70