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	$38.67	3.700%	$40.1008	$40.10	$40.10	$40.10
Purchase #2	$86.77	9.159%	$94.7173	$94.72	$94.70	$94.70
Purchase #3	$105.57	4.141%	$109.9417	$109.94	$109.95	$109.90
Purchase #4	$147.90	11.197%	$164.4604	$164.46	$164.45	$164.50
Purchase #5	$183.85	11.260%	$204.5515	$204.55	$204.55	$204.60
Purchase #6	$77.33	5.866%	$81.8662	$81.87	$81.85	$81.90
Purchase #7	$58.46	6.183%	$62.0746	$62.07	$62.05	$62.10
7 purchase totals =	$698.55		$757.7125	$757.71	$757.65	$757.80