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	$142.80	6.117%	$151.5351	$151.54	$151.55	$151.50
Purchase #2	$132.96	4.455%	$138.8834	$138.88	$138.90	$138.90
Purchase #3	$217.74	13.629%	$247.4158	$247.42	$247.40	$247.40
Purchase #4	$191.68	6.756%	$204.6299	$204.63	$204.65	$204.60
Purchase #5	$196.70	12.792%	$221.8619	$221.86	$221.85	$221.90
Purchase #6	$78.48	5.238%	$82.5908	$82.59	$82.60	$82.60
Purchase #7	$49.48	3.811%	$51.3657	$51.37	$51.35	$51.40
7 purchase totals =	$1,009.84		$1,098.2826	$1,098.29	$1,098.30	$1,098.30