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	$135.30	7.863%	$145.9386	$145.94	$145.95	$145.90
Purchase #2	$248.50	10.766%	$275.2535	$275.25	$275.25	$275.30
Purchase #3	$221.71	5.143%	$233.1125	$233.11	$233.10	$233.10
Purchase #4	$191.97	4.348%	$200.3169	$200.32	$200.30	$200.30
Purchase #5	$140.29	8.697%	$152.491	$152.49	$152.50	$152.50
Purchase #6	$172.56	12.459%	$194.0593	$194.06	$194.05	$194.10
Purchase #7	$196.47	4.616%	$205.5391	$205.54	$205.55	$205.50
7 purchase totals =	$1,306.80		$1,406.7109	$1,406.71	$1,406.70	$1,406.70