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	$139.27	13.600%	$158.2107	$158.21	$158.20	$158.20
Purchase #2	$56.45	10.476%	$62.3637	$62.36	$62.35	$62.40
Purchase #3	$192.83	3.754%	$200.0688	$200.07	$200.05	$200.10
Purchase #4	$34.39	9.159%	$37.5398	$37.54	$37.55	$37.50
Purchase #5	$104.79	6.315%	$111.4075	$111.41	$111.40	$111.40
Purchase #6	$219.95	13.858%	$250.4307	$250.43	$250.45	$250.40
Purchase #7	$220.59	7.849%	$237.9041	$237.90	$237.90	$237.90
7 purchase totals =	$968.27		$1,057.9253	$1,057.92	$1,057.90	$1,057.90