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	$67.83	12.662%	$76.4186	$76.42	$76.40	$76.40
Purchase #2	$218.51	13.210%	$247.3752	$247.38	$247.40	$247.40
Purchase #3	$52.64	11.814%	$58.8589	$58.86	$58.85	$58.90
Purchase #4	$47.35	10.827%	$52.4766	$52.48	$52.50	$52.50
Purchase #5	$228.82	5.291%	$240.9269	$240.93	$240.95	$240.90
Purchase #6	$59.28	3.195%	$61.174	$61.17	$61.15	$61.20
Purchase #7	$45.98	9.281%	$50.2474	$50.25	$50.25	$50.20
7 purchase totals =	$720.41		$787.4776	$787.49	$787.50	$787.50