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	$125.55	8.647%	$136.4063	$136.41	$136.40	$136.40
Purchase #2	$82.56	13.672%	$93.8476	$93.85	$93.85	$93.80
Purchase #3	$132.40	9.513%	$144.9952	$145.00	$145.00	$145.00
Purchase #4	$43.49	4.249%	$45.3379	$45.34	$45.35	$45.30
Purchase #5	$153.46	9.300%	$167.7318	$167.73	$167.75	$167.70
Purchase #6	$206.49	13.130%	$233.6021	$233.60	$233.60	$233.60
Purchase #7	$171.66	4.460%	$179.316	$179.32	$179.30	$179.30
7 purchase totals =	$915.61		$1,001.2369	$1,001.25	$1,001.25	$1,001.10