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	$180.59	5.222%	$190.0204	$190.02	$190.00	$190.00
Purchase #2	$134.37	6.134%	$142.6123	$142.61	$142.60	$142.60
Purchase #3	$238.78	13.739%	$271.586	$271.59	$271.60	$271.60
Purchase #4	$82.94	3.239%	$85.6264	$85.63	$85.65	$85.60
Purchase #5	$81.39	10.854%	$90.2241	$90.22	$90.20	$90.20
Purchase #6	$44.96	5.550%	$47.4553	$47.46	$47.45	$47.50
Purchase #7	$6.92	9.342%	$7.5665	$7.57	$7.55	$7.60
7 purchase totals =	$769.95		$835.0910	$835.10	$835.05	$835.10