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	$26.69	9.847%	$29.3182	$29.32	$29.30	$29.30
Purchase #2	$248.56	11.439%	$276.9928	$276.99	$277.00	$277.00
Purchase #3	$59.73	11.263%	$66.4574	$66.46	$66.45	$66.50
Purchase #4	$234.85	9.739%	$257.722	$257.72	$257.70	$257.70
Purchase #5	$172.64	3.363%	$178.4459	$178.45	$178.45	$178.40
Purchase #6	$235.57	8.584%	$255.7913	$255.79	$255.80	$255.80
Purchase #7	$80.99	12.132%	$90.8157	$90.82	$90.80	$90.80
7 purchase totals =	$1,059.03		$1,155.5433	$1,155.55	$1,155.50	$1,155.50