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	$78.35	6.701%	$83.6002	$83.60	$83.60	$83.60
Purchase #2	$206.62	10.725%	$228.78	$228.78	$228.80	$228.80
Purchase #3	$109.52	10.287%	$120.7863	$120.79	$120.80	$120.80
Purchase #4	$147.93	10.712%	$163.7763	$163.78	$163.80	$163.80
Purchase #5	$67.63	5.277%	$71.1988	$71.20	$71.20	$71.20
Purchase #6	$124.82	13.315%	$141.4398	$141.44	$141.45	$141.40
Purchase #7	$85.37	5.569%	$90.1243	$90.12	$90.10	$90.10
7 purchase totals =	$820.24		$899.7057	$899.71	$899.75	$899.70