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	$52.59	3.552%	$54.458	$54.46	$54.45	$54.50
Purchase #2	$169.76	12.106%	$190.3111	$190.31	$190.30	$190.30
Purchase #3	$40.59	6.776%	$43.3404	$43.34	$43.35	$43.30
Purchase #4	$50.61	11.682%	$56.5223	$56.52	$56.50	$56.50
Purchase #5	$236.98	4.374%	$247.3455	$247.35	$247.35	$247.30
Purchase #6	$177.65	4.435%	$185.5288	$185.53	$185.55	$185.50
Purchase #7	$76.83	9.455%	$84.0943	$84.09	$84.10	$84.10
7 purchase totals =	$805.01		$861.6004	$861.60	$861.60	$861.50