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	$115.92	13.605%	$131.6909	$131.69	$131.70	$131.70
Purchase #2	$32.95	7.163%	$35.3102	$35.31	$35.30	$35.30
Purchase #3	$113.56	13.105%	$128.442	$128.44	$128.45	$128.40
Purchase #4	$17.80	4.231%	$18.5531	$18.55	$18.55	$18.60
Purchase #5	$146.41	10.671%	$162.0334	$162.03	$162.05	$162.00
Purchase #6	$179.87	9.521%	$196.9954	$197.00	$197.00	$197.00
Purchase #7	$217.28	11.590%	$242.4628	$242.46	$242.45	$242.50
7 purchase totals =	$823.79		$915.4878	$915.48	$915.50	$915.50