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	$102.99	13.126%	$116.5085	$116.51	$116.50	$116.50
Purchase #2	$128.60	6.778%	$137.3165	$137.32	$137.30	$137.30
Purchase #3	$141.27	12.645%	$159.1336	$159.13	$159.15	$159.10
Purchase #4	$53.79	10.440%	$59.4057	$59.41	$59.40	$59.40
Purchase #5	$66.49	7.730%	$71.6297	$71.63	$71.65	$71.60
Purchase #6	$189.97	5.533%	$200.481	$200.48	$200.50	$200.50
Purchase #7	$207.48	10.724%	$229.7302	$229.73	$229.75	$229.70
7 purchase totals =	$890.59		$974.2052	$974.21	$974.25	$974.10