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	$25.50	5.470%	$26.8949	$26.89	$26.90	$26.90
Purchase #2	$123.63	5.723%	$130.7053	$130.71	$130.70	$130.70
Purchase #3	$189.49	8.764%	$206.0969	$206.10	$206.10	$206.10
Purchase #4	$178.89	4.265%	$186.5197	$186.52	$186.50	$186.50
Purchase #5	$138.91	3.178%	$143.3246	$143.32	$143.30	$143.30
Purchase #6	$196.60	9.139%	$214.5673	$214.57	$214.55	$214.60
Purchase #7	$107.64	3.587%	$111.501	$111.50	$111.50	$111.50
7 purchase totals =	$960.66		$1,019.6097	$1,019.61	$1,019.55	$1,019.60