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	$92.61	8.436%	$100.4226	$100.42	$100.40	$100.40
Purchase #2	$69.56	12.295%	$78.1124	$78.11	$78.10	$78.10
Purchase #3	$60.55	9.547%	$66.3307	$66.33	$66.35	$66.30
Purchase #4	$73.93	8.714%	$80.3723	$80.37	$80.35	$80.40
Purchase #5	$18.78	7.798%	$20.2445	$20.24	$20.25	$20.20
Purchase #6	$228.58	11.817%	$255.5913	$255.59	$255.60	$255.60
Purchase #7	$42.99	11.331%	$47.8612	$47.86	$47.85	$47.90
7 purchase totals =	$587.00		$648.9350	$648.92	$648.90	$648.90