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	$121.31	12.314%	$136.2481	$136.25	$136.25	$136.20
Purchase #2	$159.37	13.726%	$181.2451	$181.25	$181.25	$181.20
Purchase #3	$44.54	13.265%	$50.4482	$50.45	$50.45	$50.40
Purchase #4	$156.86	9.503%	$171.7664	$171.77	$171.75	$171.80
Purchase #5	$19.57	3.724%	$20.2988	$20.30	$20.30	$20.30
Purchase #6	$135.72	4.114%	$141.3035	$141.30	$141.30	$141.30
Purchase #7	$238.67	7.792%	$257.2672	$257.27	$257.25	$257.30
7 purchase totals =	$876.04		$958.5773	$958.59	$958.55	$958.50