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	$185.97	7.846%	$200.5612	$200.56	$200.55	$200.60
Purchase #2	$92.77	6.249%	$98.5672	$98.57	$98.55	$98.60
Purchase #3	$201.40	8.333%	$218.1827	$218.18	$218.20	$218.20
Purchase #4	$92.80	13.186%	$105.0366	$105.04	$105.05	$105.00
Purchase #5	$168.64	7.857%	$181.89	$181.89	$181.90	$181.90
Purchase #6	$34.49	13.697%	$39.2141	$39.21	$39.20	$39.20
Purchase #7	$115.63	10.579%	$127.8625	$127.86	$127.85	$127.90
7 purchase totals =	$891.70		$971.3143	$971.31	$971.30	$971.40