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	$106.39	5.160%	$111.8797	$111.88	$111.90	$111.90
Purchase #2	$133.48	12.837%	$150.6148	$150.61	$150.60	$150.60
Purchase #3	$28.93	5.484%	$30.5165	$30.52	$30.50	$30.50
Purchase #4	$220.86	11.377%	$245.9872	$245.99	$246.00	$246.00
Purchase #5	$14.98	4.333%	$15.6291	$15.63	$15.65	$15.60
Purchase #6	$21.47	8.473%	$23.2892	$23.29	$23.30	$23.30
Purchase #7	$11.83	13.735%	$13.4549	$13.45	$13.45	$13.50
7 purchase totals =	$537.94		$591.3714	$591.37	$591.40	$591.40