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	$37.45	5.684%	$39.5787	$39.58	$39.60	$39.60
Purchase #2	$182.71	3.779%	$189.6146	$189.61	$189.60	$189.60
Purchase #3	$172.71	4.386%	$180.2851	$180.29	$180.30	$180.30
Purchase #4	$98.59	7.309%	$105.7959	$105.80	$105.80	$105.80
Purchase #5	$97.55	6.315%	$103.7103	$103.71	$103.70	$103.70
Purchase #6	$165.48	3.716%	$171.6292	$171.63	$171.65	$171.60
Purchase #7	$101.52	10.394%	$112.072	$112.07	$112.05	$112.10
7 purchase totals =	$856.01		$902.6858	$902.69	$902.70	$902.70