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	$170.83	8.513%	$185.3728	$185.37	$185.35	$185.40
Purchase #2	$139.36	5.314%	$146.7656	$146.77	$146.75	$146.80
Purchase #3	$183.61	13.285%	$208.0026	$208.00	$208.00	$208.00
Purchase #4	$235.60	12.598%	$265.2809	$265.28	$265.30	$265.30
Purchase #5	$90.43	12.619%	$101.8414	$101.84	$101.85	$101.80
Purchase #6	$206.96	7.314%	$222.0971	$222.10	$222.10	$222.10
Purchase #7	$14.36	6.684%	$15.3198	$15.32	$15.30	$15.30
7 purchase totals =	$1,041.15		$1,144.6802	$1,144.68	$1,144.65	$1,144.70