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	$116.54	12.509%	$131.118	$131.12	$131.10	$131.10
Purchase #2	$129.86	8.851%	$141.3539	$141.35	$141.35	$141.40
Purchase #3	$59.85	3.672%	$62.0477	$62.05	$62.05	$62.00
Purchase #4	$174.48	12.644%	$196.5413	$196.54	$196.55	$196.50
Purchase #5	$78.40	12.645%	$88.3137	$88.31	$88.30	$88.30
Purchase #6	$108.57	12.450%	$122.087	$122.09	$122.10	$122.10
Purchase #7	$144.32	10.860%	$159.9932	$159.99	$160.00	$160.00
7 purchase totals =	$812.02		$901.4548	$901.45	$901.45	$901.40