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	$46.97	12.301%	$52.7478	$52.75	$52.75	$52.70
Purchase #2	$30.56	4.127%	$31.8212	$31.82	$31.80	$31.80
Purchase #3	$95.56	10.456%	$105.5518	$105.55	$105.55	$105.60
Purchase #4	$7.90	8.172%	$8.5456	$8.55	$8.55	$8.50
Purchase #5	$166.94	7.187%	$178.938	$178.94	$178.95	$178.90
Purchase #6	$115.94	8.595%	$125.905	$125.91	$125.90	$125.90
Purchase #7	$83.38	7.411%	$89.5593	$89.56	$89.55	$89.60
7 purchase totals =	$547.25		$593.0687	$593.08	$593.05	$593.00