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	$133.58	9.742%	$146.5934	$146.59	$146.60	$146.60
Purchase #2	$119.95	4.515%	$125.3657	$125.37	$125.35	$125.40
Purchase #3	$178.61	12.258%	$200.504	$200.50	$200.50	$200.50
Purchase #4	$85.69	5.729%	$90.5992	$90.60	$90.60	$90.60
Purchase #5	$223.55	10.631%	$247.3156	$247.32	$247.30	$247.30
Purchase #6	$132.73	7.146%	$142.2149	$142.21	$142.20	$142.20
Purchase #7	$247.57	3.663%	$256.6385	$256.64	$256.65	$256.60
7 purchase totals =	$1,121.68		$1,209.2313	$1,209.23	$1,209.20	$1,209.20