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	$154.38	10.162%	$170.0681	$170.07	$170.05	$170.10
Purchase #2	$34.82	3.775%	$36.1345	$36.13	$36.15	$36.10
Purchase #3	$172.88	12.531%	$194.5436	$194.54	$194.55	$194.50
Purchase #4	$143.28	13.252%	$162.2675	$162.27	$162.25	$162.30
Purchase #5	$37.62	13.788%	$42.807	$42.81	$42.80	$42.80
Purchase #6	$213.54	5.732%	$225.7801	$225.78	$225.80	$225.80
Purchase #7	$136.52	6.865%	$145.8921	$145.89	$145.90	$145.90
7 purchase totals =	$893.04		$977.4929	$977.49	$977.50	$977.50