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	$216.57	6.462%	$230.5648	$230.56	$230.55	$230.60
Purchase #2	$89.90	12.634%	$101.258	$101.26	$101.25	$101.30
Purchase #3	$93.59	5.248%	$98.5016	$98.50	$98.50	$98.50
Purchase #4	$133.27	6.146%	$141.4608	$141.46	$141.45	$141.50
Purchase #5	$104.92	6.283%	$111.5121	$111.51	$111.50	$111.50
Purchase #6	$35.79	13.270%	$40.5393	$40.54	$40.55	$40.50
Purchase #7	$156.42	13.420%	$177.4116	$177.41	$177.40	$177.40
7 purchase totals =	$830.46		$901.2482	$901.24	$901.20	$901.30