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	$141.43	3.782%	$146.7789	$146.78	$146.80	$146.80
Purchase #2	$119.39	13.118%	$135.0516	$135.05	$135.05	$135.10
Purchase #3	$196.53	8.112%	$212.4725	$212.47	$212.45	$212.50
Purchase #4	$85.81	5.731%	$90.7278	$90.73	$90.75	$90.70
Purchase #5	$197.69	10.505%	$218.4573	$218.46	$218.45	$218.50
Purchase #6	$74.35	10.285%	$81.9969	$82.00	$82.00	$82.00
Purchase #7	$104.92	6.367%	$111.6003	$111.60	$111.60	$111.60
7 purchase totals =	$920.12		$997.0853	$997.09	$997.10	$997.20