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	$77.84	11.285%	$86.6242	$86.62	$86.60	$86.60
Purchase #2	$93.30	8.218%	$100.9674	$100.97	$100.95	$101.00
Purchase #3	$71.90	11.743%	$80.3432	$80.34	$80.35	$80.30
Purchase #4	$72.93	13.411%	$82.7106	$82.71	$82.70	$82.70
Purchase #5	$47.67	5.452%	$50.269	$50.27	$50.25	$50.30
Purchase #6	$17.47	11.469%	$19.4736	$19.47	$19.45	$19.50
Purchase #7	$96.35	12.698%	$108.5845	$108.58	$108.60	$108.60
7 purchase totals =	$477.46		$528.9725	$528.96	$528.90	$529.00