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	$79.69	3.591%	$82.5517	$82.55	$82.55	$82.60
Purchase #2	$145.39	9.390%	$159.0421	$159.04	$159.05	$159.00
Purchase #3	$69.42	12.821%	$78.3203	$78.32	$78.30	$78.30
Purchase #4	$72.72	13.627%	$82.6296	$82.63	$82.65	$82.60
Purchase #5	$131.72	6.178%	$139.8577	$139.86	$139.85	$139.90
Purchase #6	$131.66	3.578%	$136.3708	$136.37	$136.35	$136.40
Purchase #7	$202.92	6.871%	$216.8626	$216.86	$216.85	$216.90
7 purchase totals =	$833.52		$895.6348	$895.63	$895.60	$895.70