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	$57.42	3.142%	$59.2241	$59.22	$59.20	$59.20
Purchase #2	$36.48	5.684%	$38.5535	$38.55	$38.55	$38.60
Purchase #3	$29.60	8.247%	$32.0411	$32.04	$32.05	$32.00
Purchase #4	$70.76	13.277%	$80.1548	$80.15	$80.15	$80.20
Purchase #5	$136.78	4.740%	$143.2634	$143.26	$143.25	$143.30
Purchase #6	$186.48	7.584%	$200.6226	$200.62	$200.60	$200.60
Purchase #7	$120.82	7.199%	$129.5178	$129.52	$129.50	$129.50
7 purchase totals =	$638.34		$683.3773	$683.36	$683.30	$683.40