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	$236.62	8.256%	$256.1553	$256.16	$256.15	$256.20
Purchase #2	$135.52	8.720%	$147.3373	$147.34	$147.35	$147.30
Purchase #3	$204.61	5.280%	$215.4134	$215.41	$215.40	$215.40
Purchase #4	$199.26	11.669%	$222.5116	$222.51	$222.50	$222.50
Purchase #5	$135.65	5.120%	$142.5953	$142.60	$142.60	$142.60
Purchase #6	$146.25	10.797%	$162.0406	$162.04	$162.05	$162.00
Purchase #7	$109.43	9.197%	$119.4943	$119.49	$119.50	$119.50
7 purchase totals =	$1,167.34		$1,265.5478	$1,265.55	$1,265.55	$1,265.50