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	$19.58	5.791%	$20.7139	$20.71	$20.70	$20.70
Purchase #2	$101.45	10.166%	$111.7634	$111.76	$111.75	$111.80
Purchase #3	$210.59	5.137%	$221.408	$221.41	$221.40	$221.40
Purchase #4	$93.47	10.358%	$103.1516	$103.15	$103.15	$103.20
Purchase #5	$250.25	12.551%	$281.6589	$281.66	$281.65	$281.70
Purchase #6	$85.82	12.748%	$96.7603	$96.76	$96.75	$96.80
Purchase #7	$248.29	3.690%	$257.4519	$257.45	$257.45	$257.50
7 purchase totals =	$1,009.45		$1,092.9080	$1,092.90	$1,092.85	$1,093.10