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	$133.60	8.691%	$145.2112	$145.21	$145.20	$145.20
Purchase #2	$119.89	6.778%	$128.0161	$128.02	$128.00	$128.00
Purchase #3	$200.89	10.192%	$221.3647	$221.36	$221.35	$221.40
Purchase #4	$86.26	5.300%	$90.8318	$90.83	$90.85	$90.80
Purchase #5	$120.53	7.256%	$129.2757	$129.28	$129.30	$129.30
Purchase #6	$14.90	3.858%	$15.4748	$15.47	$15.45	$15.50
Purchase #7	$110.58	5.241%	$116.3755	$116.38	$116.40	$116.40
7 purchase totals =	$786.65		$846.5498	$846.55	$846.55	$846.60