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	$11.40	9.342%	$12.465	$12.47	$12.45	$12.50
Purchase #2	$100.83	8.634%	$109.5357	$109.54	$109.55	$109.50
Purchase #3	$114.98	8.576%	$124.8407	$124.84	$124.85	$124.80
Purchase #4	$20.92	8.239%	$22.6436	$22.64	$22.65	$22.60
Purchase #5	$87.59	3.799%	$90.9175	$90.92	$90.90	$90.90
Purchase #6	$8.40	3.481%	$8.6924	$8.69	$8.70	$8.70
Purchase #7	$82.28	3.377%	$85.0586	$85.06	$85.05	$85.10
7 purchase totals =	$426.40		$454.1535	$454.16	$454.15	$454.10