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	$40.55	8.860%	$44.1427	$44.14	$44.15	$44.10
Purchase #2	$140.40	3.558%	$145.3954	$145.40	$145.40	$145.40
Purchase #3	$115.88	4.429%	$121.0123	$121.01	$121.00	$121.00
Purchase #4	$107.41	5.666%	$113.4959	$113.50	$113.50	$113.50
Purchase #5	$93.49	13.220%	$105.8494	$105.85	$105.85	$105.80
Purchase #6	$52.33	13.303%	$59.2915	$59.29	$59.30	$59.30
Purchase #7	$104.50	11.424%	$116.4381	$116.44	$116.45	$116.40
7 purchase totals =	$654.56		$705.6253	$705.63	$705.65	$705.50