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	$89.96	12.863%	$101.5316	$101.53	$101.55	$101.50
Purchase #2	$185.75	5.614%	$196.178	$196.18	$196.20	$196.20
Purchase #3	$116.28	11.456%	$129.601	$129.60	$129.60	$129.60
Purchase #4	$31.25	3.590%	$32.3719	$32.37	$32.35	$32.40
Purchase #5	$153.93	4.110%	$160.2565	$160.26	$160.25	$160.30
Purchase #6	$28.85	9.259%	$31.5212	$31.52	$31.50	$31.50
Purchase #7	$28.48	6.644%	$30.3722	$30.37	$30.35	$30.40
7 purchase totals =	$634.50		$681.8324	$681.83	$681.80	$681.90