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	$126.73	13.205%	$143.4647	$143.46	$143.45	$143.50
Purchase #2	$84.73	6.691%	$90.3993	$90.40	$90.40	$90.40
Purchase #3	$219.84	10.435%	$242.7803	$242.78	$242.80	$242.80
Purchase #4	$180.45	8.638%	$196.0373	$196.04	$196.05	$196.00
Purchase #5	$56.54	13.742%	$64.3097	$64.31	$64.30	$64.30
Purchase #6	$21.72	8.835%	$23.639	$23.64	$23.65	$23.60
Purchase #7	$83.97	3.842%	$87.1961	$87.20	$87.20	$87.20
7 purchase totals =	$773.98		$847.8264	$847.83	$847.85	$847.80