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	$131.67	8.249%	$142.5315	$142.53	$142.55	$142.50
Purchase #2	$112.63	3.510%	$116.5833	$116.58	$116.60	$116.60
Purchase #3	$117.50	8.870%	$127.9223	$127.92	$127.90	$127.90
Purchase #4	$77.73	4.859%	$81.5069	$81.51	$81.50	$81.50
Purchase #5	$56.37	3.307%	$58.2342	$58.23	$58.25	$58.20
Purchase #6	$141.97	6.135%	$150.6799	$150.68	$150.70	$150.70
Purchase #7	$154.44	12.378%	$173.5566	$173.56	$173.55	$173.60
7 purchase totals =	$792.31		$851.0147	$851.01	$851.05	$851.00