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	$165.80	12.105%	$185.8701	$185.87	$185.85	$185.90
Purchase #2	$15.25	7.296%	$16.3626	$16.36	$16.35	$16.40
Purchase #3	$72.92	12.473%	$82.0153	$82.02	$82.00	$82.00
Purchase #4	$75.91	6.614%	$80.9307	$80.93	$80.95	$80.90
Purchase #5	$7.79	7.667%	$8.3873	$8.39	$8.40	$8.40
Purchase #6	$169.83	5.169%	$178.6085	$178.61	$178.60	$178.60
Purchase #7	$50.83	4.801%	$53.2703	$53.27	$53.25	$53.30
7 purchase totals =	$558.33		$605.4448	$605.45	$605.40	$605.50