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	$16.40	10.121%	$18.0598	$18.06	$18.05	$18.10
Purchase #2	$197.58	12.325%	$221.9317	$221.93	$221.95	$221.90
Purchase #3	$183.65	7.111%	$196.7094	$196.71	$196.70	$196.70
Purchase #4	$62.72	11.484%	$69.9228	$69.92	$69.90	$69.90
Purchase #5	$231.48	10.839%	$256.5701	$256.57	$256.55	$256.60
Purchase #6	$197.63	10.167%	$217.723	$217.72	$217.70	$217.70
Purchase #7	$118.37	11.283%	$131.7257	$131.73	$131.75	$131.70
7 purchase totals =	$1,007.83		$1,112.6425	$1,112.64	$1,112.60	$1,112.60