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	$192.89	11.672%	$215.4041	$215.40	$215.40	$215.40
Purchase #2	$249.51	9.244%	$272.5747	$272.57	$272.55	$272.60
Purchase #3	$128.62	10.482%	$142.1019	$142.10	$142.10	$142.10
Purchase #4	$191.43	12.600%	$215.5502	$215.55	$215.55	$215.60
Purchase #5	$216.76	4.493%	$226.499	$226.50	$226.50	$226.50
Purchase #6	$16.68	12.671%	$18.7935	$18.79	$18.80	$18.80
Purchase #7	$151.94	4.361%	$158.5661	$158.57	$158.55	$158.60
7 purchase totals =	$1,147.83		$1,249.4895	$1,249.48	$1,249.45	$1,249.60