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	$42.44	12.239%	$47.6342	$47.63	$47.65	$47.60
Purchase #2	$206.63	4.605%	$216.1453	$216.15	$216.15	$216.10
Purchase #3	$151.70	9.736%	$166.4695	$166.47	$166.45	$166.50
Purchase #4	$71.36	12.592%	$80.3457	$80.35	$80.35	$80.30
Purchase #5	$249.95	12.549%	$281.3162	$281.32	$281.30	$281.30
Purchase #6	$36.86	9.533%	$40.3739	$40.37	$40.35	$40.40
Purchase #7	$131.62	11.235%	$146.4075	$146.41	$146.40	$146.40
7 purchase totals =	$890.56		$978.6923	$978.70	$978.65	$978.60