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	$17.25	6.690%	$18.404	$18.40	$18.40	$18.40
Purchase #2	$39.59	7.725%	$42.6483	$42.65	$42.65	$42.60
Purchase #3	$204.56	10.183%	$225.3903	$225.39	$225.40	$225.40
Purchase #4	$17.98	12.386%	$20.207	$20.21	$20.20	$20.20
Purchase #5	$52.80	6.592%	$56.2806	$56.28	$56.30	$56.30
Purchase #6	$174.85	8.476%	$189.6703	$189.67	$189.65	$189.70
Purchase #7	$103.87	10.710%	$114.9945	$114.99	$115.00	$115.00
7 purchase totals =	$610.90		$667.5950	$667.59	$667.60	$667.60