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	$117.33	9.278%	$128.2159	$128.22	$128.20	$128.20
Purchase #2	$172.68	13.582%	$196.1334	$196.13	$196.15	$196.10
Purchase #3	$49.35	5.188%	$51.9103	$51.91	$51.90	$51.90
Purchase #4	$96.46	9.800%	$105.9131	$105.91	$105.90	$105.90
Purchase #5	$137.64	12.871%	$155.3556	$155.36	$155.35	$155.40
Purchase #6	$142.28	11.854%	$159.1459	$159.15	$159.15	$159.10
Purchase #7	$114.56	6.457%	$121.9571	$121.96	$121.95	$122.00
7 purchase totals =	$830.30		$918.6313	$918.64	$918.60	$918.60