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	$13.39	5.561%	$14.1346	$14.13	$14.15	$14.10
Purchase #2	$135.94	10.639%	$150.4027	$150.40	$150.40	$150.40
Purchase #3	$188.91	5.807%	$199.88	$199.88	$199.90	$199.90
Purchase #4	$142.75	5.356%	$150.3957	$150.40	$150.40	$150.40
Purchase #5	$109.67	6.307%	$116.5869	$116.59	$116.60	$116.60
Purchase #6	$138.90	9.687%	$152.3552	$152.36	$152.35	$152.40
Purchase #7	$122.86	13.163%	$139.0321	$139.03	$139.05	$139.00
7 purchase totals =	$852.42		$922.7872	$922.79	$922.85	$922.80