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	$106.25	10.845%	$117.7728	$117.77	$117.75	$117.80
Purchase #2	$172.56	4.793%	$180.8308	$180.83	$180.85	$180.80
Purchase #3	$8.37	5.309%	$8.8144	$8.81	$8.80	$8.80
Purchase #4	$71.48	10.366%	$78.8896	$78.89	$78.90	$78.90
Purchase #5	$50.26	6.757%	$53.6561	$53.66	$53.65	$53.70
Purchase #6	$213.39	13.141%	$241.4316	$241.43	$241.45	$241.40
Purchase #7	$44.29	5.693%	$46.8114	$46.81	$46.80	$46.80
7 purchase totals =	$666.60		$728.2067	$728.20	$728.20	$728.20