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	$165.39	12.110%	$185.4187	$185.42	$185.40	$185.40
Purchase #2	$210.39	7.365%	$225.8852	$225.89	$225.90	$225.90
Purchase #3	$14.52	7.296%	$15.5794	$15.58	$15.60	$15.60
Purchase #4	$22.53	3.873%	$23.4026	$23.40	$23.40	$23.40
Purchase #5	$166.57	12.221%	$186.9265	$186.93	$186.95	$186.90
Purchase #6	$42.81	9.116%	$46.7126	$46.71	$46.70	$46.70
Purchase #7	$37.88	6.794%	$40.4536	$40.45	$40.45	$40.50
7 purchase totals =	$660.09		$724.3786	$724.38	$724.40	$724.40