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	$131.49	5.808%	$139.1269	$139.13	$139.15	$139.10
Purchase #2	$248.39	3.182%	$256.2938	$256.29	$256.30	$256.30
Purchase #3	$171.29	13.783%	$194.8989	$194.90	$194.90	$194.90
Purchase #4	$30.59	5.672%	$32.3251	$32.33	$32.35	$32.30
Purchase #5	$155.93	13.226%	$176.5533	$176.55	$176.55	$176.60
Purchase #6	$59.58	10.582%	$65.8848	$65.88	$65.90	$65.90
Purchase #7	$159.86	10.300%	$176.3256	$176.33	$176.35	$176.30
7 purchase totals =	$957.13		$1,041.4084	$1,041.41	$1,041.50	$1,041.40