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	$125.90	10.334%	$138.9105	$138.91	$138.90	$138.90
Purchase #2	$100.32	9.562%	$109.9126	$109.91	$109.90	$109.90
Purchase #3	$138.28	4.173%	$144.0504	$144.05	$144.05	$144.10
Purchase #4	$90.63	10.307%	$99.9712	$99.97	$99.95	$100.00
Purchase #5	$103.43	7.583%	$111.2731	$111.27	$111.25	$111.30
Purchase #6	$182.86	7.807%	$197.1359	$197.14	$197.15	$197.10
Purchase #7	$95.58	5.643%	$100.9736	$100.97	$100.95	$101.00
7 purchase totals =	$837.00		$902.2273	$902.22	$902.15	$902.30