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	$153.33	9.741%	$168.2659	$168.27	$168.25	$168.30
Purchase #2	$102.58	4.671%	$107.3715	$107.37	$107.35	$107.40
Purchase #3	$207.54	5.493%	$218.9402	$218.94	$218.95	$218.90
Purchase #4	$89.79	9.548%	$98.3631	$98.36	$98.35	$98.40
Purchase #5	$90.35	12.292%	$101.4558	$101.46	$101.45	$101.50
Purchase #6	$63.96	3.404%	$66.1372	$66.14	$66.15	$66.10
Purchase #7	$62.67	6.113%	$66.501	$66.50	$66.50	$66.50
7 purchase totals =	$770.22		$827.0347	$827.04	$827.00	$827.10