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	$50.50	7.771%	$54.4244	$54.42	$54.40	$54.40
Purchase #2	$194.81	7.107%	$208.6551	$208.66	$208.65	$208.70
Purchase #3	$244.77	11.665%	$273.3224	$273.32	$273.30	$273.30
Purchase #4	$159.63	10.839%	$176.9323	$176.93	$176.95	$176.90
Purchase #5	$215.77	5.725%	$228.1228	$228.12	$228.10	$228.10
Purchase #6	$111.77	3.366%	$115.5322	$115.53	$115.55	$115.50
Purchase #7	$73.37	12.344%	$82.4268	$82.43	$82.45	$82.40
7 purchase totals =	$1,050.62		$1,139.4160	$1,139.41	$1,139.40	$1,139.30