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	$42.51	6.208%	$45.149	$45.15	$45.15	$45.10
Purchase #2	$99.98	9.678%	$109.6561	$109.66	$109.65	$109.70
Purchase #3	$68.98	3.344%	$71.2867	$71.29	$71.30	$71.30
Purchase #4	$177.90	9.263%	$194.3789	$194.38	$194.40	$194.40
Purchase #5	$131.39	5.419%	$138.51	$138.51	$138.50	$138.50
Purchase #6	$145.98	10.294%	$161.0072	$161.01	$161.00	$161.00
Purchase #7	$11.44	12.804%	$12.9048	$12.90	$12.90	$12.90
7 purchase totals =	$678.18		$732.8927	$732.90	$732.90	$732.90