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	$74.46	10.248%	$82.0907	$82.09	$82.10	$82.10
Purchase #2	$31.31	7.865%	$33.7725	$33.77	$33.75	$33.80
Purchase #3	$44.49	13.470%	$50.4828	$50.48	$50.50	$50.50
Purchase #4	$102.69	9.703%	$112.654	$112.65	$112.65	$112.70
Purchase #5	$19.45	4.822%	$20.3879	$20.39	$20.40	$20.40
Purchase #6	$235.52	13.829%	$268.0901	$268.09	$268.10	$268.10
Purchase #7	$124.31	5.540%	$131.1968	$131.20	$131.20	$131.20
7 purchase totals =	$632.23		$698.6748	$698.67	$698.70	$698.80