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	$19.54	3.729%	$20.2686	$20.27	$20.25	$20.30
Purchase #2	$240.57	13.721%	$273.5786	$273.58	$273.60	$273.60
Purchase #3	$54.54	9.859%	$59.9171	$59.92	$59.90	$59.90
Purchase #4	$174.84	3.767%	$181.4262	$181.43	$181.45	$181.40
Purchase #5	$242.45	4.759%	$253.9882	$253.99	$254.00	$254.00
Purchase #6	$107.86	8.112%	$116.6096	$116.61	$116.60	$116.60
Purchase #7	$149.70	3.239%	$154.5488	$154.55	$154.55	$154.50
7 purchase totals =	$989.50		$1,060.3371	$1,060.35	$1,060.35	$1,060.30