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	$29.32	7.190%	$31.4281	$31.43	$31.45	$31.40
Purchase #2	$91.68	5.424%	$96.6527	$96.65	$96.65	$96.70
Purchase #3	$163.53	11.326%	$182.0514	$182.05	$182.05	$182.10
Purchase #4	$79.61	13.784%	$90.5834	$90.58	$90.60	$90.60
Purchase #5	$176.43	7.378%	$189.447	$189.45	$189.45	$189.40
Purchase #6	$150.39	9.628%	$164.8695	$164.87	$164.85	$164.90
Purchase #7	$18.61	11.753%	$20.7972	$20.80	$20.80	$20.80
7 purchase totals =	$709.57		$775.8293	$775.83	$775.85	$775.90