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	$138.96	13.692%	$157.9864	$157.99	$158.00	$158.00
Purchase #2	$19.92	13.106%	$22.5307	$22.53	$22.55	$22.50
Purchase #3	$206.64	4.380%	$215.6908	$215.69	$215.70	$215.70
Purchase #4	$80.66	7.618%	$86.8047	$86.80	$86.80	$86.80
Purchase #5	$139.92	8.266%	$151.4858	$151.49	$151.50	$151.50
Purchase #6	$78.96	13.770%	$89.8328	$89.83	$89.85	$89.80
Purchase #7	$84.66	7.144%	$90.7081	$90.71	$90.70	$90.70
7 purchase totals =	$749.72		$815.0393	$815.04	$815.10	$815.00