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	$39.54	3.240%	$40.8211	$40.82	$40.80	$40.80
Purchase #2	$145.49	10.508%	$160.7781	$160.78	$160.80	$160.80
Purchase #3	$220.83	13.366%	$250.3461	$250.35	$250.35	$250.30
Purchase #4	$136.31	12.630%	$153.526	$153.53	$153.55	$153.50
Purchase #5	$162.58	10.452%	$179.5729	$179.57	$179.55	$179.60
Purchase #6	$239.77	11.150%	$266.5044	$266.50	$266.50	$266.50
Purchase #7	$171.95	5.463%	$181.3436	$181.34	$181.35	$181.30
7 purchase totals =	$1,116.47		$1,232.8922	$1,232.89	$1,232.90	$1,232.80