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	$93.57	6.728%	$99.8654	$99.87	$99.85	$99.90
Purchase #2	$75.42	8.520%	$81.8458	$81.85	$81.85	$81.80
Purchase #3	$125.78	13.655%	$142.9553	$142.96	$142.95	$143.00
Purchase #4	$207.44	7.748%	$223.5125	$223.51	$223.50	$223.50
Purchase #5	$111.96	7.564%	$120.4287	$120.43	$120.45	$120.40
Purchase #6	$137.34	5.310%	$144.6328	$144.63	$144.65	$144.60
Purchase #7	$232.66	13.140%	$263.2315	$263.23	$263.25	$263.20
7 purchase totals =	$984.17		$1,076.4720	$1,076.48	$1,076.50	$1,076.40