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	$7.83	8.751%	$8.5152	$8.52	$8.50	$8.50
Purchase #2	$224.80	11.295%	$250.1912	$250.19	$250.20	$250.20
Purchase #3	$250.92	4.874%	$263.1498	$263.15	$263.15	$263.10
Purchase #4	$132.70	13.673%	$150.8441	$150.84	$150.85	$150.80
Purchase #5	$61.41	9.810%	$67.4343	$67.43	$67.45	$67.40
Purchase #6	$103.27	9.250%	$112.8225	$112.82	$112.80	$112.80
Purchase #7	$49.57	13.518%	$56.2709	$56.27	$56.25	$56.30
7 purchase totals =	$830.50		$909.2280	$909.22	$909.20	$909.10