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	$124.32	13.273%	$140.821	$140.82	$140.80	$140.80
Purchase #2	$191.62	13.473%	$217.437	$217.44	$217.45	$217.40
Purchase #3	$101.49	12.662%	$114.3407	$114.34	$114.35	$114.30
Purchase #4	$51.56	8.419%	$55.9008	$55.90	$55.90	$55.90
Purchase #5	$152.26	9.498%	$166.7217	$166.72	$166.70	$166.70
Purchase #6	$115.58	13.573%	$131.2677	$131.27	$131.25	$131.30
Purchase #7	$241.87	11.664%	$270.0817	$270.08	$270.10	$270.10
7 purchase totals =	$978.70		$1,096.5706	$1,096.57	$1,096.55	$1,096.50