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	$71.96	8.138%	$77.8161	$77.82	$77.80	$77.80
Purchase #2	$103.61	12.522%	$116.584	$116.58	$116.60	$116.60
Purchase #3	$21.36	7.839%	$23.0344	$23.03	$23.05	$23.00
Purchase #4	$242.52	12.113%	$271.8964	$271.90	$271.90	$271.90
Purchase #5	$183.54	7.275%	$196.8925	$196.89	$196.90	$196.90
Purchase #6	$200.91	9.699%	$220.3963	$220.40	$220.40	$220.40
Purchase #7	$197.63	3.752%	$205.0451	$205.05	$205.05	$205.00
7 purchase totals =	$1,021.53		$1,111.6648	$1,111.67	$1,111.70	$1,111.60