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	$29.90	9.628%	$32.7788	$32.78	$32.80	$32.80
Purchase #2	$8.99	5.837%	$9.5147	$9.51	$9.50	$9.50
Purchase #3	$118.85	3.797%	$123.3627	$123.36	$123.35	$123.40
Purchase #4	$55.59	9.742%	$61.0056	$61.01	$61.00	$61.00
Purchase #5	$101.42	12.418%	$114.0143	$114.01	$114.00	$114.00
Purchase #6	$164.58	12.563%	$185.2562	$185.26	$185.25	$185.30
Purchase #7	$115.74	6.664%	$123.4529	$123.45	$123.45	$123.50
7 purchase totals =	$595.07		$649.3852	$649.38	$649.35	$649.50