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	$117.26	5.284%	$123.456	$123.46	$123.45	$123.50
Purchase #2	$224.36	11.861%	$250.9713	$250.97	$250.95	$251.00
Purchase #3	$181.45	12.375%	$203.9044	$203.90	$203.90	$203.90
Purchase #4	$157.63	13.500%	$178.9101	$178.91	$178.90	$178.90
Purchase #5	$181.68	8.225%	$196.6232	$196.62	$196.60	$196.60
Purchase #6	$96.92	5.153%	$101.9143	$101.91	$101.90	$101.90
Purchase #7	$250.88	9.650%	$275.0899	$275.09	$275.10	$275.10
7 purchase totals =	$1,210.18		$1,330.8692	$1,330.86	$1,330.80	$1,330.90