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	$37.81	11.821%	$42.2795	$42.28	$42.30	$42.30
Purchase #2	$158.90	5.301%	$167.3233	$167.32	$167.30	$167.30
Purchase #3	$198.29	12.806%	$223.683	$223.68	$223.70	$223.70
Purchase #4	$131.88	5.781%	$139.504	$139.50	$139.50	$139.50
Purchase #5	$233.94	3.715%	$242.6309	$242.63	$242.65	$242.60
Purchase #6	$220.86	9.577%	$242.0118	$242.01	$242.00	$242.00
Purchase #7	$129.81	3.226%	$133.9977	$134.00	$134.00	$134.00
7 purchase totals =	$1,111.49		$1,191.4302	$1,191.42	$1,191.45	$1,191.40