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	$156.76	5.185%	$164.888	$164.89	$164.90	$164.90
Purchase #2	$181.54	4.565%	$189.8273	$189.83	$189.85	$189.80
Purchase #3	$149.68	4.736%	$156.7688	$156.77	$156.75	$156.80
Purchase #4	$102.81	4.211%	$107.1393	$107.14	$107.15	$107.10
Purchase #5	$11.89	13.813%	$13.5324	$13.53	$13.55	$13.50
Purchase #6	$160.59	7.267%	$172.2601	$172.26	$172.25	$172.30
Purchase #7	$12.34	12.653%	$13.9014	$13.90	$13.90	$13.90
7 purchase totals =	$775.61		$818.3173	$818.32	$818.35	$818.30