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	$138.75	12.794%	$156.5017	$156.50	$156.50	$156.50
Purchase #2	$249.43	8.140%	$269.7336	$269.73	$269.75	$269.70
Purchase #3	$88.98	12.590%	$100.1826	$100.18	$100.20	$100.20
Purchase #4	$45.46	10.820%	$50.3788	$50.38	$50.40	$50.40
Purchase #5	$196.71	4.685%	$205.9259	$205.93	$205.95	$205.90
Purchase #6	$230.34	5.869%	$243.8587	$243.86	$243.85	$243.90
Purchase #7	$64.82	7.176%	$69.4715	$69.47	$69.45	$69.50
7 purchase totals =	$1,014.49		$1,096.0528	$1,096.05	$1,096.10	$1,096.10